I don’t know if the grapheneOS camera lets you scan anything (phone lost charge) but it might since it also has a QR code scanner option. Have you searched Fdroid?
Use Clear Scan with internet permission blocked or removed. Nothing will trouble you further.
Like for making PDFs of physical documents? It's not open source, but the Google Drive app can scan documents. It works fine, in my experience.
Yeah, Drive is one option but I'm hoping for something where I can just save PDFs to the device or share directly rather than saving to Drive.
I know its not foss and Microsoft is the devil but Office lens let's you save to the device directly in a lot of formats like pdf, word or as pictures