keybase is unfortunately one of those programs that combine many things into one - somewhat antithetical to the Unix philosophy of doing one thing well.

For kbfs, tahoe-lafs is a nice alternative. I don't know about the fuse interface as I haven't used it, but it has some solid fundamentals behind it, actively being developed and can be self hosted.

GPG still works! GPG also is a swiss army knife, unfortunately. There is OpenBSD signify (or minisign) if you want signatures.

There is also age - https://github.com/FiloSottile/age