I filed a bug report - just described what was happening. I didn't attach a project (it's not mine to share), but I linked to this thread,
GRR! I just checked and the ticket I raised can't be found. WTAF?
ash69
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Done the same. If you need to launch under Rosetta (due to 3rd party binary issues) use
arch -x86_64 /Applications/Xcode12.app/Contents/MacOS/Xcode