The Holy Spirit would, according to John 16:13. Then why are there so many Christian Churches and denominations?
13 When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own, but will speak whatever he hears, and he will declare to you the things that are to come.
People forget that this was spoken by Jesus to His One Church. The HS does guide individual believers, but only within what He has revealed to the Church.
Later the Apostle John also writes of those who departed from the Apostolic Teaching:
19 They went out from us, but they did not belong to us; for if they had belonged to us, they would have remained with us. But by going out they made it plain that none of them belongs to us. (I John 2)
He also writes about those who reject the Apostolic authority"
“(Diotrephes and Demetrius) I have written something to the church; but Diotrephes, who likes to put himself first, does not acknowledge our authority.” 3 John 1:9
Those who refuse to acknowledge the authority Jesus gave to the Apostles have always rebelled, and “gone out from us”.
Is there a some truths exist? If not, most part of called Christians are not guided by the Holy Spirit? Or what. Why.
Yes, a Truth exists.
Yes, Christians are guided by the HS, but those who depart from the One Faith, given to the Apostles and preserved infallibly in the Church by the HS, are not protected from going astray.