When installed via deb package, gallery-viewer uses general python binary, not python 3.
$ gallery-viewer
zsh: /usr/local/bin/gallery-viewer: bad interpreter: /usr/bin/python: no such file or directory
$ python --version
zsh: command not found: python
$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.3 LTS"
When installed via deb package, gallery-viewer uses general python binary, not python 3.