Tough question.
Let’s first look to see if it is a sin. There are two passages that indicate that not only is it a sin, but it is one that sees recipients, thrown into hell.
Revelation 14
9 And another, a third angel, followed them and spoke with a loud voice: “If anyone worships the beast and its image and receives a mark on his forehead or on his hand, 10 he will also drink the wine of God’s wrath, which is poured full strength into the cup of his anger. He will be tormented with fire and sulfur in the sight of the holy angels and in the sight of the Lamb, 11 and the smoke of their torment will go up forever and ever. There is no rest day or night for those who worship the beast and its image, or anyone who receives the mark of its name. 12 This calls for endurance from the saints, who keep God’s commands and their faith in Jesus.”
Revelation 19
9 Then I saw the beast, the kings of the earth, and their armies gathered together to wage war against the rider on the horse and against his army. 20 But the beast was taken prisoner, and along with it the false prophet, who had performed the signs in its presence. He deceived those who accepted the mark of the beast and those who worshiped its image with these signs. Both of them were thrown alive into the lake of fire that burns with sulfur.
We note from Revelation 19, that the Mark of the Beast is perpetrated by a deception. That does not excuse the recipient, after all Eve was deceived by the serpent, and yet, still bore the punishment. This suggest however, that for many people, this was not voluntary. We know from Revelation 13, that the Mark is virtually forced on everyone. By forced, we mean significant pressure is brought to bear by restricting their income or business. One can scarcely think that a restriction on buying or selling would be the only restriction placed on refuseniks. However, that does not mean they are aware it is the Mark.
For example, note that the Mark is introduced in chapter 13, however the warning not to take it is not until the following chapter, immediately after being told of the judgement about to come on the Whore. This, among other reasons shows that the Mark and the pharmaceutical deception that causes the economic collapse of the Whore (Rev 18:23) are contemporaneous events and both labelled deceptions. It is virtually certain that the Mark and the pharmaceutical deceptions are one and the same.
Revelation 14 appears to make a very complete blanket statement, anyone who receives the Mark will receive the wrath of God. However, there are other similar passages in Revelation that also make blanket statements about the consequences of specific sins. Revelation 9 and 16 talk about those who will not repent of soceries “pharmekia”, sexual immorality, thefts,. Revelation 21 specifically lists all liars, idolators, sorcerers, cowards, etc. will have their part in the Lake of Fire. Damning evidence.
However, we know that for these sins listed, we are called to repentance, and that God does forgive these sins, while at the same time the condemnation of those who commit such sins can be repented. Jesus says there is only one unforgivable sin: “Blasphemy of the Holy Spirit” (Mark 3:22-30). Without a direct connection, that neither the Apostle John, nor the angel revealing this, allude to.
Some have argued, that receiving the Mark is akin to Blasphemy of the Holy Spirit, and is a deliberate sin in defiance of God. This does not square with that the Mark is delivered with a deception – most will not know that the Mark is “The Mark”. Did the Pharisees know they had committed Blasphemy of the Holy Spirit? Not by name, but they did know they were attributing a good work of God, to Satan. There is nothing in Scripture that suggests that the Mark of the Beast is akin, or a form of, Blasphemy of the Holy Spirit.
Therefore, the weight of Scripture indicates that the Mark of the Beast, can be repented from, but most will not, just as most will not repent of their porn, sexual immorality, thefts, lies, idol worship, sorcery, etc. Those who do not, will go into the Lake of Fire.
N.B.
I shared last night with a recent Bible College graduate the wrestlings I have in communicating the material on this site, and how Christians are extremely reluctant to even discuss it. It got on to the issue of the Mark of the Beast and he sadly said that he will be going to hell, if it is the Mark, because he took the vax. He then attempted to argue that Scripture was clear that this was a type of “final sin” and akin to Blasphemy of the Holy Spirit. I’m not sure I persuaded him that it was not blasphemy of the Holy Spirit.
My message to this young man, and to all who took the Mark/Vax. It is not blasphemy of the Holy Spirit. Accept that you were deceived, and repent. Do not, cling to the deception as many have done saying “I was obeying the government” or “I was loving my neighbour”, or “I was following the science™”. If you took the Mark to keep buying and selling, or to provide for your family, repent that you did not trust the Lord who freely gives all things to provide for you. All these reasons were part of the deception, and should be repented from.