I have the same issue on both an Intel and on a Ryzen mini PC with thunderbolt. On the new kernel (6.8.8) the Thunderbolt network adapter doesn't work, on kernel 6.8.4 it does work.
On both the 6.8.8 and the 6.8.4 I see the following in dmesg:
thunderbolt 0-1: new device found, vendor=0x5a...