It looks like the macOS 12.2.1 update has fixed the Thunderbolt Ethernet adapter issues. My Apple 27" Thunderbolt LED display's Ethernet adapter (showing as Display Ethernet in macOS Network properties) has been working for 3 days straight with DHCP enabled without having disconnected after the 14" MacBook Pro goes to sleep. Hopefully, the issue has been fixed.
I'm still having occasional flashing of the Apple's 27" Thunderbolt LED display (picture on / picture off) after the Mac wakes up from sleep, which I first noticed in macOS 12.1, but a simple disconnect of the Thunderbolt cable between the Mac and the Thunderbolt 4 dock and then reconnecting of the cable fixes that problem. That screen flashing problem doesn't occur every time after the Mac wakes up from sleep, but it's annoying.
Overall, I think I'm going to change my approach to upgrading macOS going forward. Apple seems to be incapable of releasing stable major macOS versions, with something breaking after every early dot release. The only reason I went with Monterey was that the 14" MacBook Pro came with Monterey. If the obvious bugs in Monterey get fixed by next summer/fall, I will stick with Monterey and not upgrade to the next macOS version next fall. I think I will start upgrading to the next major macOS release one year behind the release of the .0 version. It seems to me that the new macOS gets pretty stable with most bugs squashed right before the scheduled release of the next major version (which is usually in early fall).