good-old `ZXing` ( https://github.com/zxing/zxing ) does the job for me nicely, supports non-QR codes, and contains practically zero BS. The only downside IMO is the forcefully-narrowed scan window, which can cause complications with extremely large QR codes, as the pixels get a little blurry and decoding gets harder for the software.

Edit: you can find it on Fdroid or probably on the project site/page. It's not getting updates, but why would my QR scanner need those, anyways..... also Google doesn't want it to be published anymore, iirc due to it using relatively ancient APIs.