It’s a whole ordeal to get set up. There’s some plugins for Calibre, I believe one is called NoDRM and os is called De-DRM. Can’t remember which one I’m using or what the differences are.

From Google Play Books you can download the encrypted books (from the website on PC). You are supposed to use Adobe Digital Editions with your Google login to be able to read the encrypted/DRM-protected books on your PC. When you’ve set up Adobe Digital Editions, you can find a key file somewhere (can’t remember the location, you should be able to Google that) which you can use together with one of the plugins in Calibre. And that should normally be it.

That didn’t work for me though. So I found some other third party DRM removal tool, in which I logged in with my Google/Adobe Digital Editions account. It could then decrypt the books, but more importantly, it also made a key file somewhere, which i WAS able to use in Calibre. So now, with that key file, I can just drag the encrypted books directly into Calibre, and it decrypts them just fine.

It’s been several years, so I’ve probably forgotten or misremembered some details.

EDIT: By the way, there seems to be a time limit on decrypting the downloaded books, so download them from Google and decrypt them withing relatively short time (a few hours maybe, not sure). Don’t think you can just decrypt them whenever in the future.