Here is the section from the catechism that AVZ continually misrepresents and a fuller understanding thereof, emphasis mine:
The Church and non-Christians
839 "Those who have not yet received the Gospel are related to the People of God in various ways."325
The relationship of the Church with the Jewish People. When she delves into her own mystery, the Church, the People of God in the New Covenant, discovers her link with the Jewish People,326 "the first to hear the Word of God."327 The Jewish faith, unlike other non-Christian religions, is already a response to God's revelation in the Old Covenant. To the Jews "belong the sonship, the glory, the covenants, the giving of the law, the worship, and the promises; to them belong the patriarchs, and of their race, according to the flesh, is the Christ",328 "for the gifts and the call of God are irrevocable."329
840 And when one considers the future, God's People of the Old Covenant and the new People of God tend towards similar goals: expectation of the coming (or the return) of the Messiah. But one awaits the return of the Messiah who died and rose from the dead and is recognized as Lord and Son of God; the other awaits the coming of a Messiah, whose features remain hidden till the end of time; and the latter waiting is accompanied by the drama of not knowing or of misunderstanding Christ Jesus.
841 The Church's relationship with the Muslims. "The plan of salvation also includes those who acknowledge the Creator, in the first place amongst whom are the Muslims; these profess to hold the faith of Abraham, and together with us they adore the one, merciful God, mankind's judge on the last day."330
842 The Church's bond with non-Christian religions is in the first place the common origin and end of the human race:
All nations form but one community. This is so because all stem from the one stock which God created to people the entire earth, and also because all share a common destiny, namely God. His providence, evident goodness, and saving designs extend to all against the day when the elect are gathered together in the holy city. . .331
843 The Catholic Church recognizes in other religions that search, among shadows and images, for the God who is unknown yet near since he gives life and breath and all things and wants all men to be saved. Thus, the Church considers all goodness and truth found in these religions as "a preparation for the Gospel and given by him who enlightens all men that they may at length have life."332
844 In their religious behavior, however, men also display the limits and errors that disfigure the image of God in them:
Very often, deceived by the Evil One, men have become vain in their reasonings, and have exchanged the truth of God for a lie, and served the creature rather than the Creator. Or else, living and dying in this world without God, they are exposed to ultimate despair.333
845 To reunite all his children, scattered and led astray by sin, the Father willed to call the whole of humanity together into his Son's Church. The Church is the place where humanity must rediscover its unity and salvation. The Church is "the world reconciled." She is that bark which "in the full sail of the Lord's cross, by the breath of the Holy Spirit, navigates safely in this world." According to another image dear to the Church Fathers, she is prefigured by Noah's ark, which alone saves from the flood.334
325 LG 16.
326 Cf. NA 4.
327 Roman Missal, Good Friday 13:General Intercessions,VI.
328 Rom 9:4-5.
329 Rom 11:29.
330 LG 16; cf. NA 3.
331 NA 1.
332 LG 16; cf. NA 2; EN 53.
333 LG 16; cf. Rom 1:21, 25.
334 St. Augustine, Serm. 96,7,9:PL 38,588; St. Ambrose, De virg. 18 118:PL 16,297B; cf. already 1 Pet 3:20-21.
First to note is the line I made larger above, which states that all must enter the Church to find salvation.
Secondly, to properly read the Catechism, sometimes it is absolutely necessary
to follow the footnotes to get the true sense of what is actually being said. In this case, let's follow footnote 430 which pertains to the paragraph in question. "LG" refers to the document Lumen Gentium, and "NA" refers to the document "Nostra Aetate".
From Lumen Gentium, emphasis mine:
16. Finally, those who have not yet received the Gospel are related in various ways to the people of God.(18*) In the first place we must recall the people to whom the testament and the promises were given and from whom Christ was born according to the flesh.(125) On account of their fathers this people remains most dear to God, for God does not repent of the gifts He makes nor of the calls He issues.(126) But the plan of salvation also includes those who acknowledge the Creator. In the first place amongst these there are the Muslims, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge mankind.Nor is God far distant from those who in shadows and images seek the unknown God, for it is He who gives to all men life and breath and all things,(127) and as Saviour wills that all men be saved.(128) Those also can attain to salvation who through no fault of their own do not know the Gospel of Christ or His Church, yet sincerely seek God and moved by grace strive by their deeds to do His will as it is known to them through the dictates of conscience.(19*) Nor does Divine Providence deny the helps necessary for salvation to those who, without blame on their part, have not yet arrived at an explicit knowledge of God and with His grace strive to live a good life. Whatever good or truth is found amongst them is looked upon by the Church as a preparation for the Gospel.(20*) She knows that it is given by Him who enlightens all men so that they may finally have life. But often men, deceived by the Evil One, have become vain in their reasonings and have exchanged the truth of God for a lie, serving the creature rather than the Creator.(129) Or some there are who, living and dying in this world without God, are exposed to final despair. Wherefore to promote the glory of God and procure the salvation of all of these, and mindful of the command of the Lord, "Preach the Gospel to every creature",(130) the Church fosters the missions with care and attention.
So we see that CCC #841 is a restatement of part of LG 16, the part that I have bolded above. Here is the other reference.
From Nostra Aetate, emphasis mine:
3. The Church regards with esteem also the Moslems. They adore the one God, living and subsisting in Himself; merciful and all- powerful, the Creator of heaven and earth,(5) who has spoken to men; they take pains to submit wholeheartedly to even His inscrutable decrees, just as Abraham, with whom the faith of Islam takes pleasure in linking itself, submitted to God. Though they do not acknowledge Jesus as God, they revere Him as a prophet. They also honor Mary, His virgin Mother; at times they even call on her with devotion. In addition, they await the day of judgment when God will render their deserts to all those who have been raised up from the dead. Finally, they value the moral life and worship God especially through prayer, almsgiving and fasting.
Since in the course of centuries not a few quarrels and hostilities have arisen between Christians and Moslems, this sacred synod urges all to forget the past and to work sincerely for mutual understanding and to preserve as well as to promote together for the benefit of all mankind social justice and moral welfare, as well as peace and freedom.
5. Cf St. Gregory VII, letter XXI to Anzir (Nacir), King of Mauritania (Pl. 148, col. 450f.)
Notice the footnote here, #5. Again we follow the footnote to get the context of this quote. How exactly do we as Catholics believe that Muslims "adore the one true God"?
From St. Gergory VII, letter XXI to Anzir (Nacir), King of Mauritania:
"God, the Creator of all, without whom we cannot do or even think anything that is good, has inspired to your heart this act of kindness. He who enlightens all men coming into this world (John 1.9) has enlightened your mind for this purpose. Almighty God, who desires all men to be saved (1 Timothy 2.4) and none to perish is well pleased to approve in us most of all that besides loving God men love other men, and do not do to others anything they do not want to be done unto themselves (cf. Mt. 7.14). We and you must show in a special way to the other nations an example of this charity, for we believe and confess one God, although in different ways, and praise and worship Him daily as the creator of all ages and the ruler of this world. For as the apostle says: "He is our peace who has made us both one." (Eph. 2.14) Many among the Roman nobility, informed by us of this grace granted to you by God, greatly admire and praise your goodness and virtues... God knows that we love you purely for His honour and that we desire your salvation and glory, both in the present and in the future life. And we pray in our hearts and with our lips that God may lead you to the abode of happiness, to the bosom of the holy patriarch Abraham, after long years of life here on earth.
So in conclusion, Muslims "adore the one true God" ONLY insofar as they 1) recognize him as creator and ruler of the world, 2) believe that he is merciful and 3) seek goodness and virtue. They are deceived people but as persons who were created by God, God wills them to be saved, and so in a certain way gives them certain shadows and graces to lead them to goodness and truth and beauty, just as He does ALL men. We DESIRE their salvation and true happiness which they can only find in Christ Jesus and not in Islam.
There is only one God and that God has made himself manifest in various ways to all men, at the very least naturally. The satanic deception given to Mohammed has only created a source of deception leading many of God's created people away from him in certain ways. They as people recognize certain true things about God, but have been taught other things that are false which enslave them.
In summary, yes 841 when deprived of context loses the full truth of what is implied by that statement. In the fullness of Catholic teaching (that is, taking into account the WHOLE catechism and the documents that the Catechism draws upon), Muslims are simply partially deceived people who God wants to save, and that salvation can be found in Christ Jesus and his Church, into which both may enter through Christian baptism. Islam doesn't save them. God is drawing them to himself through truth and goodness and beauty, just as He is drawing all persons, and those three things are ultimately found only in the Catholic Church.