Thanks rickcurran, I'll try! I just upgraded my Xcode to Version 12.2 (12B45b) and can confirm that the "Mac" checkbox xcode is indeed there now.

Actually... I'm still getting the error: Dear Developer, We identified one or more issues with a recent delivery for your app, "MyAppName" 2.1 (2). Your delivery was successful, but you may wish to correct the following issues in your next delivery: ITMS-90863: Apple silicon Macs support issue - The app has LSApplicationLaunchProhibited set to true. This is not supported on Mac. After you’ve corrected the issues, you can upload a new binary to App Store Connect. Best regards, The App Store Team

@emasie Here's the screenshot, hope it helps and please keep us posted! imgur.com/MeiBvXa