Well you can install alternative app stores on iOS Devices without jailbreaking. Essentially all you need is a profile for that app store, the entire ecosystem of enterprise Device management in built on this mechanism which provides custom app stores to enterprises.

No, you can't distribute apps directly to customers. That's why Facebook's certificate got revoked by Apple.

[1] https://arstechnica.com/gadgets/2019/01/facebook-and-google-...

I wasnt aware of this!