Is the best practice of using the Thread class based on that it has less overhead and in turn offers better performance compared to Dispatch or is there other reasoning behind this? What would the downsides be of using a higher level API?

That makes sense. Exactly what are you referring to when you mean explicit threading? Would you recommend using continuations to bridge tasks from the higher level parts of the app to the render engine? In my use case I'm doing a lot of Core Image render tasks and displaying the results in MTKViews.

I'm also seeing this issue with Big Sur. In my case I am using a MTKView via NSViewRepresentable as my app is built using SwiftUI. MTLCreateSystemDefaultDevice will not trigger the display to use the discrete GPU. It returns the discrete GPU but the display is still using the integrated. My machine also has the AMD Radeon Pro 560 and the Intel(R) HD Graphics 630. Opening Pixelmator Pro will immediately trigger the switch to the discrete GPU and when closing the display switches back to the integrated. Any feedback would be most appreciated!