I would install desktop Linux on my iPhone if I could but there are no drivers in mainline and they work hard to lock the bootloader down (and before someone suggests android, the intention there is just as bad but tends to be less well executed and there still aren’t suitable drivers available.)
I mean the Librem 5 "works" in the way you describe.
I don't think you're going to really be able to reliably avoid the problem that very very very few people outside of AOSP are doing any work on OSS for phones.
An argument can be made that it's morally wrong, but if you're going down that road, there's a lot of things should be morally more compelling than Apple's AppStore policies.