I agree that the simplest solution is to insist and make updates until your app is approved.
Another option that should be listed here, is to ask the client to purchase an enterprise certificate. This will allow you to distribute the app outside of the app store.
Erel, about this: "ask the client to purchase an enterprise certificate" - Thanks for this interesting solution, but in this case I don't think it's possible (unfortunately), because the client is a public body (not a private client) and the timing of budgeting approval for anything is biblical (to put it mildly).
Currently, to facilitate the needs of the end customer for the "very first launch of the app", I am proposing to add the QRCode of the TestFlight app to the Android QRCode, specifying two important things:
1) currently the iOS version is in Beta version.
2) However, it can be installed with a specific instructions
Of course, I also specified to the end customer that the "TestFlight" version has a duration of 90 days.
At the moment it is the only solution (in my opinion) that can satisfy the customer. I'm wrong ?