First tip - Back everything up first just in case things go wrong.
Second tip - BACK IT UP FIRST!! Seriously - BACKUP. Music is precious
If I was doing it, I’d turn to MP3TAG first. https://www.mp3tag.de/en/index.html
You can load your albums into that program and copy ARTIST and ALBUM name into the tags first from the folders.
There is a FILENAME to TAG mode.
Give it a string like %artist%\%album%\%track%
Pick a couple of albums to experiment. And USE THE PREVIEW MODE to check results.
That will pull in the artist, album and TrackNumber from the folder and file names and preload some of the tags.
Once you have the pattern correct on a couple of albums, you can hit a larger bulk of folders.
After doing that, this should then give Picard a far better chance of getting tracks identified using CLUSTER and LOOKUP.
And finally SAVE the results to write the new tags.
Big tip - always work on small numbers of albums at a time with Picard so you can check the results.