Average Pro,
I have never been able to reconnect my QNAP TVS-872XT NAS via Thunderbolt over I.P. since installing Big Sur. I tried the NAS refresh icon in Qfinder Pro that you referred to, but it would not reconnect the NAS via Thunderbolt.
I contacted Apple Enterprise Level support and I have been working with a support fellow named Kevin for the last two weeks. He has collected a lot of system diagnostic data, and forwarded it to Apple Engineers. Last Friday he told me the Apple Engineers had "opened an investigation" and that any resolution of this issue would likely come through a Big Sur update. Kevin has admitted the the problem is not a QNAP problem but is a problem with Big Sur, and since I did NOT have the problem with Catalina, I can certainly confirm that.
Furthermore, I have this exact same problem with an iMac Pro that is connected via Thunderbolt to my TVS-872XT NAS -- again indicating that it is a MacOS problem and not a QNAP problem since once again the problem did not exist under Catalina.
Quite honestly I do not believe that Apple will ever resolve this problem. Fortunately my Mac Pro 7.1 has two 10Gb ethernet ports so I have directly connected one of the 10Gb ethernet ports of my NAS with my Mac Pro 7.1. The 10Gb ethernet port is not lost or is restored when the Mac Pro wakes from sleep, and the data transfer speeds with 10 GbE are as fast if not faster than thunderbolt over I.P. To obtain a high speed connection to my iMac Pro which does not have two 10GbE ports, I shall have to buy an expensive 10GbE switch and the proper high bandwidth ethernet cables, which I am reluctant to do since this is just a secondary machine.
I am surprised that QNAP support support did not tell you immediately that dropping the Thunderbolt connection was an Apple MacOs problem and that they could provide no help. That is what they told me when I opened a ticket on the issue. I believe QHAP Support is telling the truth because (a) the problem did not exist under Catalina and (b) the vocal synthesizer on my TVS-872XT reports that Thunderbolt has been connected every time I wake my Mac Pro from sleep, but MacOS does not see the the Thunderbolt connection, only the far slower 1 GbE connection.
I'll certainly keep you posted on any further developments and I hope that tyou will do the same for me.
Tom