Same issue for me. I am on Catalina. But after updating Xcode from 12.3 to 12.4 the performance lost is heavy and everything that worked good, now ist very very slow. I hope Apple is fixing this.

Sorry for my delayed answer. I've tried the terminal command, but with no success. Now, there is a new error message: "TimeoutError: Timed out waiting for connection to DTServiceHub after 15.0 seconds." The problem is, that i can't manage to send the zip. Here is my attached file (the summary text) from diagnostics: previews_diagnostics_summary.txt Thank you

Hi, yes i've send the feedback via FB9983188. Hoping for a solution — Noem less than a minute ago

So after looking in several threads I assume that there is a problem with older hardware (specially the gpu) and Monterey / newer Xcode versions. I don't know which gpu you are using but older ones have problems with OpenCL (which looks like Xcode is using). If you have a discrete and internal gpu try the following: -Open the Simulator or launch it -Under File/GPU Selection choose "Prefer integrated GPU" (this will only use the internal gpu of your Mac.) -Close Simulator and Xcode and try it again with newer Simulators like 13.4 or above. (But be aware that the performance is lower than with the external gpu)