Upgraded to Big Sur, and Xcode 12.3, now cannot run simulator

Just upgraded after running on Mojave for several years. Now with Xcode 12.3, I cannot run any simulator.

[APP] architectures (arm64) include none that iPhone 12 can execute (Intel 64-bit).

No matter what I try, I cannot change the architectures and have it work. It is set to "$(ARCHS_STANDARD)". Changing build active architecture changes nothing either.