This repo hosts an unofficial flatpak version of Keybase
Keybase is an encrypted messenger and file sharing software.
However, file sharing (in particular access to the /keybase file system) is not supported by this flatpak.
This package is not on the official flathub, so you'll have to download, build, and install it yourself. Clone the git repo, and then run:
flatpak-builder --user --install --force-clean builddir io.keybase.Keybase.yml
Now you can run it like any other flatpak.