https://alternativeto.net/software/office-lens/?license=opensource

Looks like there may be a few more, haven't used any of them though.

I use this on a daily basis on Android, works pretty well & is available through Fdroid:

https://github.com/LittleTrickster/PDF-Doc-Scan

And it (OpenScan) was never on par with Lens, at the best of times. I hate MS with a long-burning passion, but Lens was best in class. Nothing matched its whiteboard scanning; it was absolutely indispensable, in the pre-COVID times.

Lens is the one thing I still use from Microsoft. None of the competition works nearly as well for b&w/greyscale plus angle correction and multiple PDF pages.

On top of that it is completely local, doesn't make you sign into an account, doesn't ask for location access, and doesn't phone home (at least what I have been able to see).

The only thing that Microsoft makes that I will choose over open source alternatives. Knock on wood that they don't change it.

I haven't come across a FOSS scanner app that comes close to the performance abd features of the popular closed source ones. That's why I use closed source ones that still work when I deny them internet access. Genius Scan and Microsoft Lens both work that way.

i don't think this is foss https://play.google.com/store/apps/details?id=com.notebloc.app

it has ads, but you can pay one time to remove them.