Simulators do not show for an SwiftUI App

On a MBP with Catalina.

When using Xcode 12 (any release), and open a SwiftUI app (absolutely basic one, just a say hello), I get the usual list of simulators.

If I open the same app with any Xcode below 12 (e.g 11.6, 11.5), I do not see any simulator in the list.

Any other app (SwiftUI or pure Swift) has no problem.

I tried to add simulators, could not get it done.

What could be corrupted in the SwiftUI app ?
Simulators do not show for an SwiftUI App
 
 
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