System is a Mac mini 2018, i7 6 core, 64GB, 2TB, updated Monterey, RX 5700 XT eGPU.
Problem was that every Topaz app presented a blank screen when launched. Unchecking “prefer external GPU” in the Get Info box fixed it - at the cost of usually not using the eGPU. Tried a bunch of workarounds, no luck. The problem happens with daVinci Resolve, Silverfast 9, and other apps.
What finally worked is to plug the main monitor into an eGPU video output instead of into the Mini. Then launching with “prefer external GPU” checked works fine.
I speculate that MacOS turns off the integrated GPU when eGPU is checked. But that seems to cut off the app’s window in the main display - oops!
This has never happened on my MacBook Air M2 - which of course has no eGPU capability.