There's an OCR app available right in F-droid that I've been using, works great!
https://f-droid.org/en/packages/io.github.subhamtyagi.ocr/
It runs on the open-source, offline Tesseract 5 OCR engine.
Definitely do not rely Google, you know they're archiving everything, and while DeepL is probably safe enough (assuming you're not OCRing... idk, your credit card) it is still closed-source, as has been mentioned.
There is another company with free online OCR apps called Aspose. It's open source so you could give that a look, but it's not something that would work offline.