To follow up on this, I now have an answer, which is that Apple did accept my app into the App Store. ADHG - Yes, in general, Mac Catalyst apps can be distributed outside the App Store. However apparently this is not possible for apps that link against HomeKit. These have to go through the App Store.

Anticro - Apple have added HomeKit support for Catalyst in Big Sur. If you get the latest Xcode beta and Big Sur beta you can start using HomeKit in your Catalyst app :) As per my original question though, what I'm concerned about is whether Apple will allow an app into the App Store that doesn't really have many features itself, but rather acts as a bridge between a macOS app and HomeKit. It seems like this should be allowed, but I haven't been able to determine this for sure.

Well this is embarrassing, it turns out that this is my bug. In putting everything together for the feedback report, I checked over this code again and I found an error. I'm reading an 8-byte value from the file which is an epoch time. Instead of doing: int64_t val=0; read(fd,&val,8); I was doing: int64_t val=0; read(fd,&time,8); I'm surprised this code didn't crash before, considering its stupidity! Many thanks Quinn, you have been extremely helpful.

Many thanks for your quick reply Quinn! Attached are two full crash reports from two different machines. Thanks again, Ben Crash Log 1 - https://developer.apple.com/forums/content/attachment/42e1f2fe-32e4-478c-96bf-b1ec8cc1824d Crash Log 2 - https://developer.apple.com/forums/content/attachment/47b57154-5640-4f5b-8e6e-dd12251a8143