While microsoft has admitted to bugs causing exactly this scenario. I personally have a stabe 6 months with dual-boot. And only updating cachos once a month or every two weeks has been fine. The server and rog ally exclusively runs linux.
0xf
It is 90% arch, except for the few packages it has in it's own repository. I have it on two pc's and I have used arch for years I can not say it's any different from a stability perspective. I almost never have issues on arch but also I wouldn't recommend cachyos to anyone who had issues with arch. Couse I definitely had to remove custom packages just to fix dependency issues etc.
Yes, most likely need to compile it yourself. Or the distros would need a v1,v2,v3,v4 version. Also you need to know the feature set of you cpu. Distros will probably compile with the lowest common denominator, since those are compatible largest range of cpu's. Cachyos does compile it's packages for v3 optimization, I don't think that needs avx512. So can definitely see some distros trying something out.
Use steam, setup a desktop profile in settings while in desktop. https://docs.bazzite.gg/Handheld_and_HTPC_edition/Handheld_Wiki/ search for desktop controls.