I called Apple support today to report this as a bug and also requested assistance in downgrading macOS 12.1 to 12.0.1, but Apple told me there is no way to downgrade the M1 Mac. All of these scenarios worked fine with macOS 12.0.1 before I upgraded it to 12.1. I tried to connect the same Thunderbolt2-to-GigabitEthernet adapter directly to the 14' M1 Pro MacBook Pro (by daisy-chaining to to the Apple Thunderbolt3-to-Thunderbolt2 adapter), and I get the same issue - the adapter can't get a DHCP lease.

I also have an Apple Thunderbolt2-to-GigabitEthernet adapter (dongle), which I tried to connect to the Thunderbolt2 port on the 27' Apple Thunderbolt Display, but I can't even get a DHCP lease on this adapter after the restart. With macOS 12.1 running on the 14' M1 Pro MacBook Pro, when the MacBook Pro goes to sleep and then I wake it up a few minutes later, it takes a while for the 'Display Ethernet' connection to detect that it has a cable connected to it, and once it detects the cable, it can't get a DHCP lease so it goes to self-assigned IP address .x. I had it cabled to a switch and it worked fine until I upgraded to macOS 12.1. One of the monitors that I have connected to my 14' M1 Pro MacBook Pro is the 27' Apple Thunderbolt Display, which has a built-in Gigabit Ethernet adapter.

Last night I upgraded to macOS 12.1 from 12.0.1, and I'm having issues with Thunderbolt-based Gigabit adapters with the 14' M1 Pro MacBook Pro.

Mac ethernet to thunderbolt