I’ve just tried. Indeed, the command for listing the user doesn’t output anything.
For the version, it works but you have to write photoprism --version in the command (so the same as yours, but with – before version).
To answer your question: it’s currently not possible to add users. It should be possible soon™ (currently, the photoprism package is verry old; it will be updated when Yunohost upgrades to Bookworm, but there is no ETA for that).