I have not been able to monitor dGPU temps since moving to OpenCore. I have to trust that the video card is cooling itself sufficiently. Personally, I did my overclocking and know how the video card behaves when I was still on Clover + FakeSMC. If I ever needed to mess with a new video card, I can see myself going back to FakeSMC to do my testing.
If you want to try switching to FakeSMC, just delete all references to VirtualSMC in config.plist > Kernel > Add and add FakeSMC and its plugins along with all their Executable Paths and Plist Paths. That's it.
Yes, the sensors are very different between VirtualSMC and FakeSMC. When switching between them, it confuses iStat Menus to the point where I have to redo my menu bar.
VirtualSMC has enough sensors for CPU for me to know if everything is running within tolerances. It just lacks and dGPU sensors.