I share in OPs "unexpected ejections" of external drives and experience random crashes/sleep for up to a minute or two of ethernet port several times every day on a new Studio Ultra which came with what would be a called a fresh install of Monterey. I didn't "migrate" from my older Intels and instead went to the trouble of manually moving files I actually wanted onto the new one and installing only apps that I actually use again from the App Store, etc. It's the cleanest possible way to migrate and minimize bringing accumulated kludge from older Macs.
Unexpected ejection and random ethernet reboots(?) persist with 12.6.1. I've been testing at each point upgrade and even had foolish hope that just maybe this latest point-point upgrade might fix these bugs. Nope. Many "unexpected ejections" in the last 2 days- some as quick as only a few minutes, two where an enclosure made it for about 5 hours. The SAME enclosure with the SAME cable connected to either Intel Mac running macOS BEFORE Big Sur was stable for a few YEARS and is stable again when I test to rule out that the enclosure itself is going bad.
It looks like hope turns to Ventura finally getting around to putting the "universal" back in USB on Macs.
Personally, I think the ethernet issue is directly related... that all ports have momentary "blinks" of sleep/crash & reboot and thus, while many enclosures can roll with such blinks, others "unexpectedly eject." I suspect port management code itself has a bug(s) and those quick blinks of ethernet may be the culprit behind potential quick blinks of USB too. That's personal speculation based on the best deduction I can do and may be entirely wrong. However, I strongly suspect if I could boot this Ultra with a macOS BEFORE Big Sur, both problems would be resolved.
OP should note: not ALL enclosures unexpectedly disconnect and I don't see tons of posts about my ethernet observation either (though there are certainly many more than only mine)... so a good idea if you are interested is to either backup your existing internal to a bootable external or install latest Monterey on an external and boot into that to try latest Monterey with your own mix of hardware. If it works fine with your stuff (be sure to give it a few days at least), consider making it permanent. If not, it's the easiest way to switch back to a macOS version that is more stable for your needs.
If I get tempted to gamble on Ventura, that's how I'll do it through at least 3 or 4 point upgrades. Hypothetically, Ventura should bring many optimization for Silicon Macs including Ultra so it is VERY TEMPTING to go for it.
