I own all the PF2 rulebooks on Demiplane, but I also own a ton of 3rd party rulebooks, mostly from Roll For Combat, which add a ton of character build options.
Their books obviously have PDF versions, but that’s not directly useful with Demiplane. Same with their Foundry VTT versions.
That said, they do publish .json files meant for import into Pathbuilder.
It would be cool if we could upload Pathbuilder-style json to add new options to Demiplane’s character builder, because as things stand right now, it seems unlikely anyone in my groups would use Demiplane PF2 builder when so many options are missing.