We've been shipping a B2B, PWA-enabled web app to iOS Safari users for almost 2 years and it all mostly "just works" now. We even have a customer using hand-written provisioning profiles via Azure InTune to roll out PWA web apps to their iPad home screens automatically.
To be fair, figuring out how to do this is not documented in any meaningful way whatsoever. I had to reverse engineer another PWA that already worked on iOS/Safari in order to figure out the right path.
If anything, Apple should be punished for intentionally obfuscating the capabilities of their products. I feel like this is where they are going to weasel their way out of trouble in court - "Oh look if you do this <performs elaborate ceremony no rational person could conceive> then you can actually achieve an open application ecosystem on apple devices".
Are there resources you can recommend to other PWA developers? It sounds like there are many people in this thread that haven't pieced it together like you've been able to.