The best “solution” is to just use the website instead of the app. Even with all of the flaws of the website, I still prefer it to the app. (To be fair, I haven’t used the app in years now, so maybe it has improved by now - but looking at the complaints people still post about the app, probably not.)
The radical solution would be to add pdf support to Playnite. Playnite can already play emulated games in an emulator, and a pdf viewer could be treated as an “emulator” to run pdf “games”. Looking at https://api.playnite.link/docs/manual/features/emulationSupport/addingNewEmulators.html, this shouldn’t be all that difficult to do with the technical skills.