I have confirmed on both a 2017 iMac Pro and a late 2019 Mac Pro 7.1 that installing Big Sur 14.3 update breaks Thunderbolt over I.P. and the Macs with Big Sur 14.3 connected via Thunderbolt to my QNAP NAS TVS-872XT will not boot. The boot progress stops and hangs about half-way through. Removing the Thunderbolt connection from the NAS to the Mac and the Mac will boot with no problems. Apple broke Thunderbolt over I.P. in Big Sur 14.0 and 14.1, then restored it in 14.2 and have now broken it again in 14.3. If you have a NAS connected via Thunderbolt, I would strongly advise against installing the Big Sur 14.3 update.
Tom
Tom