I am running Resolve Studio 17 on an M1 Mac Mini with Big Sur 11.3 and my UltraStudio Monitor 3G does not work. It's plugged in via Thunderbolt 3 and the power light is on, but Resolve or Desktop Video (v12) does not see it.
This has been discussed twenty times in the other subforums - Security settings are different in newer OS X like Big Sur. Take a look there for the details.