For macOS universal binaries, yes, they still build both platforms. For iOS, it's only ever building for the platform you target, simulator or device, so the only change there is the simulator is now an arm64 target.
Typically in debug mode "Active Architecture Only" is set to "Yes." This means for most local builds you'll only have been building one architecture regardless of platform
This applies to incremental and clean builds running locally with default Xcode settings
When you archive and build for the store then your compilation will include all architectures
This applies to incremental and clean builds running locally with default Xcode settings
When you archive and build for the store then your compilation will include all architectures