The PDF was/is a closed-source propriety file format.

If you really wanted to leave the Apple eco-system, it would most likely be possible to run macos in an emulator (kvm/qemu) on a pc and most likely the software too.

forget me not, i think on f-droid may be an option. it’s fairly easy to make data files for, and you could easily ask your favourite llm to wrap some data into the format.

Bad how? Slow to respond, poor knowledge, or just non-existant ticketing?

I considered an accounting SaaS once. Only once though. The amount of constantly changing regulations would make it a very high maintenance project.