I've listened to enough podcasts about QAnon that nothing here was really new, but if you are curious about where it got started and how it spread, this is a good primer. The best part was at the end: supportive answers for concerned friends and family members whose relationships have been destroyed. It boils down to general cult advice:
1. Don't argue, it's useless and only entrenches someone further in their beliefs. Facts obviously don't matter to someone who believes this stuff, so there's no point in bringing them up.
2. If you feel up to it, try to find a point of common doubt about the Q universe. The book gives several ideas, but one example is: Why did Q use a janky porn message board to communicate this very important information? I'd like to think of more questions like this for Q-fringe believers, eg people who believe the stuff peddled on Fox but don't realize that it comes from QAnon and don't even understand what Q is exactly.
3. Keep communication open - you might be the only link to reality that this person has if they ever do have a doubt they would like to talk about. But this doesn't mean you have to accept listening to the latest conspiracy theories or politics. Try to stick to conversations about good memories you had together in the past (preferably pre-Q).
4. Go outside with them. Literally. Try to get out of cell signal range and connect with nature.

Good luck this holiday season, folks!