the fact the millions of gun owners would not comply and revolt

I hope so but I have doubts. It would be a slow boiling of the frog like so many other things. Just like with speech online, they would start with going after people who seem kind of reasonable to go after to most people. Like they'd start by just confiscating the guns of a few outright Hitler hailing "death to all jews, race war now" people to see the reaction from the public. Then do it to a larger group of the same type of people. Then go after the ones who are white supremacists but who are saying "no violence, work within the system". Maybe they'll even confiscate from some Antifa types in order to decrease the angry reaction from the right. Then they'll go after people who are not exactly all white supremacists but still more edgy than Tucker Carlson. Like the "Groypers". They'll just gradually work their way out like that.

Even if a large group did decide to revolt, it seems that the government does not need to be too concerned about a revolt that would actually threaten their power because they have thoroughly infiltrated the opposition. It's interesting that both of the groups (Proud Boys and Oath Keepers) that are being charged for conspiracy in relation to Jan 6 had a federal agent or asset in leadership.

Another thing, I notice that even many people who are very pro second amendment only go as far as to say that they'll shoot any ATF agent who tries to take from them. In other words, stand by while they're taking from other people. Hopefully enough would defend their own guns to make the law unenforceable but realistically, there could eventually be a need for some people to "aim higher" than the boots on the ground enforcers. And it will be increasingly harder to get away with something like that as surveillance and government use of AI increases.

Side note to any feds reading: No, I am not planning to "aim higher" myself. Lol.