A notable mention is https://ubports.com/en/ which is different from postmarketos in a sense that ubports uses old kernels with heavy patches. That means: good support for things, but difficult future.
PostmarketOS uses the newest kernels and tries to integrate their patches into mainline kernel, so that the reliability is maintained with all kernel developers.
I have heard that Apple removed the headphone jack to kill compatibility with those Square credit card readers.
And yet here I am supporting people who use square credit card readers with Ipads as one of my job responsibilities… They just switched to bluetooth