There are a wide range of topics for disagreement. Clear infringement on basically every human right, slavery, is one end of that range. I've never heard any MAGA people supporting slavery.
Many of the primary areas of political disagreement are much more nuanced and both sides (yep, I said it) have valid concerns IF people take the time to try to listen to what is being said. Their concerns are sometimes based in lies that they've been convinced are true but, in their mind, they often believe they are doing what's right for the country.
Perhaps you've figured out my general intellectual approach to these types of issues, but I will spell it out in more detail.
1. First, establish some basic principles on which we can agree. When I am speaking to someone who is making a categorical denial -- or who is at least using that language -- often the first step is to establish that the categorial denial is wrong, and that there are clearly some situations that fall outside the principle.
Thus we have now agreed that your initial statement about people losing friendships over politics was incomplete. That's fine. We can't always be complete about everything in advance, and sometimes the instinct to be complete creates long posts and people don't like that. So I'm not slamming on you. We're just in agreement now that there exist at least some political issues over which termination of friendship is valid and indeed morally required to avoid complicity.
2. Slavery is a clear example of that, which is why I bring it up. Using non-controversial examples is a good way of talking about the underlying theory and basic contours of discussion. Obviously slavery is orders of magnitude more oppressive, violent and evil than anything we are seeing today. That's good! Likewise, I don't detect much enthusiasm for opening death camps like in Nazi Germany. That's good! I would argue that being friends with anyone holding either of those noxious positions is itself evil.
3. So now our task becomes a bit simpler. We can ask, is what we are seeing now essentially like slavery, or so categorically different that it's more or less irrelevant. And again, there are obvious, non-controversial examples on the other side. Some people like to use "economic development" zones in efforts to stimulate struggling economies. Others note that those programs generally don't work, in part because they are designed more as vehicles for graft and/or tax handouts to rich people for doing what they were going to do already. I don't think anyone thinks of this disagreement as akin to slavery. So good!
4. And thus we have to ask whether MAGA behavior, and the things that MAGA supports, are more like economic development zones or more like slavery or fascism. I would say it's more like the latter. The economic development zones type of policy never appealed to MAGA, not really. That's why MAGA emerged. Nobody wanted what Mitt Romney was selling. What really gets MAGA going are the culture war issues, and those invariably involve some form of government oppression. Again, not nearly as bad as slavery! But still bad.
5. So my tentative -- very tentative -- conclusion is that it is perfectly valid to weaken or eliminate friendships based on some form of political disagreement. For slavery, you cannot be friends with a slaveholder without being complicit, and shunning/exiling/cancelling the slaveowner is a moral imperative. For MAGA, I would not say that it is a moral imperative to oppose it, except in the more extreme manifestations. But it is certainly valid, acceptable and unsurprising that one would might do so -- if for no other reason than MAGA rants are extremely unpleasant and frustrating.
Where, if anywhere in this list of points, do you disagree?