My favourite tool on Windows to do that is fre:ac.
I should mention, however, the benefits of flac audio depend of the equipment and the person listening. Me, personally, I can’t, no matter what I do, tell the difference between a 245 kbps VBR mp3, and a cd-quality flac, even when doing side-by-sides. So, I think that it’s not worth wasting time and storage space using flacs.
I have a samsung s9 running android 10. Everything works, so it’s probably not a critical issue. Still, I got android 14 running with noble rom and it worked perfectly, besides banking apps.