I confirm the statement made above by killerbob. Since I installed 11.3 beta 3, the Thunderbolt bridge feature stopped working with my QNAP TVS-872xT connected in "DAS" mode. When I revert to 11.2.3, it works again.
I tested 11.3b4 and b5 - no change unfortunately. I checked this on both my Imac 2020, and on my MBP 2019.
Looking forward to a fix - I re-connected through a standard RJ-45 for now.....