I wanted to give it a try, but attempting to build a Debian package fails.

$ dpkg-buildpackage

...

gpg: skipped "John Factotum <50942278+johnfactotum@users.noreply.github.com>": No secret key gpg: dpkg-sign.LHxm7FS6/com.github.johnfactotum.foliate_1.4.0.dsc: clear-sign failed: No secret key

dpkg-buildpackage: error: failed to sign .dsc file

edit: build does indeed work and I could use the viewer, building a Debian package fails though.