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

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

NSProcess beginActivityWithOptions:reason: for example.

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

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

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

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

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

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.

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