Some ARE working, but because the Envoy Express wasn't working, I assumed all my TB3 devices were not hot plugging. The UltraFine now hot plugs under Monterey. I'm not sure when this started, but that's another one that did not hot plug when I built the system. TS3+ dock and the UltraFine monitor do hot plug. Anything I hot plug with the Apple TB3/2 adapter, however, does not hot plug under Monterey or Big Sur. I also tested the Apple Gigabit adapter under Big Sur, and it does not hot plug under 11.6.5 or 11.6.6. My ProArt TB firmware is still showing 31.49 under thunderbolt bus in Big Sur.
Funny, the one device I really want hot plug for (envoy express) is the one that won't work.