Well, that was fun
You can’t use Paizo’s setting, either. Sorry to disappoint!If I'm ever able to get some more experience for PF2 under my belt, I'd love to write some 3pp/fan-created material for it. The tools for developers seem much more generous than what is provided by 5e.
Like I tried to adapt an old adventure series I wrote to 5e, only to find numerous things aren't available to use unless you publish on DMs Guild - and then you have to use Forgotten Realms and aren't allowed to change certain things of the setting, cosmology, history, etc.