Mr_Ed provides a nice, fairly mainstream list of bugs that affect many. And I bet others could add many more. I'll add just one more that has lingered since Big Sur...
This is widespread but not affecting
every user and
every external enclosure. It's referenced in
countless threads here, there and everywhere ... including Apple's own support forums (do searches for "macOS unexpected ejections" to discover the breadth & depth of this issue).
When someone shares the problem, defenders will try to redirect to cables, blame the user, user settings, firmware updates, etc... while ignoring large numbers of posts of people who upgraded to a macOS version newer than Big Sur and crashed into this problem with a previously perfectly-reliable enclosure(s) and all else remaining the
same... and then- because they needed the enclosure more than the updated macOS FABs- DOWNGRADE to a pre-Big Sur macOS version again and the enclosure resumes being perfectly stable (and/or hooking the
same enclosure with the same cable/firmware/etc to ANY older Mac or any PC and it being perfectly stable too). All of the redirect blame variables remain the same here- just one thing changes.
Hop on Amazon and select an enclosure of interest: pick an enclosure, any enclosure. Then search reviews for "macOS unexpected ejection" and see if you can find one with no references of buyers claiming it does this. Good luck. It's harder than you think unless you focus on those with hardly any reviews.
I'm towards 95% convinced that this is port management bug(s) in macOS based upon a ton of testing including the perfect stability through the same cable connection to older Macs (running pre-Big Sur macOS) or PCs but not being able to remain connected for more than about 3 hours to any "latest & greatest" Mac running latest & greatest(?) macOS versions.
We're on about 5
YEARS of this now. Is Apple ever going to debug port management software in macOS??? The DIY, workaround is basically enclosure roulette: keep trying different ones until you luck out with one that can stay connected... even though the ones you have are fine with older Macs and any PC.
My opinion: bring on that Snow Leopard year
or two!
Significantly debug what we have instead of glomming on a bunch of new stuff every year whether many of us want it or not.