That's incredibly disappointing. Vote here to signal the importance of a Linux client for Proton Drive. A Linux client is currently the top feature request for Proton Drive that has not yet been implemented.
Why I stopped paying for unlimited. I uploaded about 100GB of files to Proton Drive years ago at 1MB upload speed through the browser and its STILL way too slow. Even downloading the files takes forever!
I had to setup a Windows VM to get faster speeds through their app to recover my files from being locked in the cloud. Not worth it.