Can’t link mp3 files to iTunes

I know there have been posts like this before, and I’ve scoured the internet trying to find a fix that works and haven’t been able to find one, even after a couple of hours of trying. I’m not able to link files to iTunes when I previously was able to upload an mp3 around six months ago just fine. I updated iTunes and my iPhone to the latest versions so I don’t think that’s an issue. I was also able to upload the mp3 file to my iTunes library just fine, but dragging and dropping doesn’t work, nor does going to File > Add File To Library. Tried several different YouTube to mp3 converters and used one from another post called mp3-now that someone else said had worked. The blue outline shows up when I try to link the file and when I reload iTunes I’m able to see the file “in” my phone’s library, just not uploaded. I’m really scratching my head because I haven’t had a problem with this previously. Any help would be appreciated.