Cryptomator is a multi-platform transparent client-side encryption of your files in the cloud.
Assuming flatpak, flatpak-builder, and git packages are installed, follow the next steps:
$ git clone https://github.com/purejava/flathub.git
$ cd flathub/
$ flatpak remote-add --if-not-exists --user flathub https://flathub.org/repo/flathub.flatpakrepo
$ flatpak-builder build --force-clean --install-deps-from=flathub org.cryptomator.Cryptomator.yaml
$ flatpak-builder --user --install --force-clean build org.cryptomator.Cryptomator.yaml
$ flatpak run org.cryptomator.Cryptomator
# ...to uninstall the artifact
$ flatpak uninstall --delete-data --user org.cryptomator.Cryptomator
# ...and to clean-up everything
$ rm -rf .flatpak-builder/ build/
$ flatpak uninstall --unused --user
$ flatpak remote-delete --user flathub