rclone has support for Proton Drive. It’s in beta I think. Unfortunately Protons API isn’t published so rclone’s implementation is a reverse engineered one and may not be reliable long term.
Also disclaimer: I haven’t tried out rclone. Haven’t had time to set it up yet
I’m on Bitwarden right now and have been thinking of switching to KeePass. My issue keeping me from actually switching is the convenience factor. Can’t imagine making it even more annoying to use for my SO