Enable the "Main Thread Checker" and see if you are calling some AppKit methods from the wrong thread.

Feral Interactive Hitman 2016 port had the same issue, because the application name contained the ™ character. But on macOS 11.3 beta 2 I can run it, so probably it has been fully or partially fixed (tested only on AMD gpu).

Add --options=runtime to your codesign invocation.

Did you check if MTLResourceStorageModeShared is supported on Sierra and High Sierra on the GPU your testers are using?

An optical cable haven't got enough bandwidth to transmit 6 channels of PCM audio. It can only do 6 channels of AC3 or DTS. I don't remember if the AppleTV will automatically convert it to AC3 if you set it to do so in the AppleTV settings.

That's because you selected SwiftUI in the Interface popup. SwiftUI can only be used with Swift.

No, the 15% or 30% cut is only for the App Store.

I would try to run Xcode 10 on an earlier macOS version. It has never been tested on Big Sur.

Does OBS set the kVTCompressionPropertyKey_DataRateLimits encoding session property? Using that property is the proper way to set an hard limit on the bitrate.

The deployment target is a combobox, you can manually type the macOS version you want into it.

NSProcess beginActivityWithOptions:reason: for example.

Yes, FFmpeg hwaccel can use a VideoToolbox hardware decoder, and hardware encoders are supported too. Check the FFmpeg documentation.

Sign and notarise it using your Developer ID certificate and then distribute it in the way you want: https://developer.apple.com/developer-id/

I remember reading somewhere that kext are not supported on macOS VM on M1. But I can't find the source of this information or where I read it.

It would be easier to just bundle a copy of those libs inside each app. Then you won't need a .pkg to install them, or a deinstaller to remove them. Anyway, if the libraries you replace in your /Libraries/MyAppLibs/ folder are properly signed, there shouldn't be any issue. Each .app bundle or library outside an .app bundle is a separate entity. Changing one entity won't affect the others, just make sure you keep using the same signing identity. Changing something inside a .app bundle will break its signature, macOS doesn't check it every time, but the next time it will (and it will surely will) the app won't run anymore.