Same except I'm debugging an actual macOS app. Big Sur and same Xcode version runs fine.

Also on DTK, no way to update from macOS 11.0 (20A5299w). After about 10 seconds I get "Download failed" and a reference to checking internet connection which is fine. I also see that on the left side bar there is this note: "Updates for this mac are managed externally ..." Not entirely certain what that means. Perhaps the updates are pushed? Total guess there.