I learned this by accident trying to clean up my 95% full gdrive account. If you request a full dump of all your Google data (search how to do it, the option is buried), then they’ll take a few days and then send you a link to download tons of zip files. These contain everything you’ve put on google, but you can narrow it down before export. One of the things in my data dump? Every piece of music I’d ever uploaded to Google music!

I forgot all about them! Recovered tons of old moms! However, huge caveat, they untagged every file and throw them all into a huge mess of numerically named files. I had to use library management tools to look up and retag all the files. Huge pain in the ass, but nice to have my old music back!