This issue also found storyboard textField, numberFormatter, and Decimal Style selection. I open lagacy project on Xcode13, build, then comma separator does not work.

Good news!? macOS 12.0.1 Monterey based build shows good decimal format results. Xcode is still Version 13.0, 13A233. Its' funny experiences but I have to say OK. It's only checked on storyboard, I'm not sure SwiftUI.