Nah it was a while back. IIRC there were multiple sources, but I don’t remember any of them 🙃
Though, I don’t really remember the details either. Maybe it was OS specific? I know there was a dodgy FUSE implementation out there for macOS at some point, and Cryptomator mounts its local drive with FUSE. I use macOS and NixOS, so it coulda been that.
Fun fact: Base64url is not quite the same as base64. Its alphabet is slightly different from base64 so its characters can be used in more places (URLs, filenames, etc.).
I suppose the tool’s name is more clear for those who are aware of those differences, but very unclear for others.
https://datatracker.ietf.org/doc/html/rfc4648#section-5