I wrote an app for myself and my co-workers to make part of our job easier. There are about a dozen people who would use this app. I tried to submit it to the App Store but it was rejected with the message that I should use custom distribution. Using the Apple Business Manager requires registering a business and getting a DUNS number, but that's overkill for what I'm doing. I'm not selling the app or running a business, I'm just sharing something useful that I built.
Neither TestFlight nor Ad Hoc distribution seem to be the right tool for this job. The users are not technical and the app should update like a normal app.
What is the correct way to go about doing this?