Any idea why flatpack doesn’t remove unused (automatically installed) dependencies automatically or at least give a hint, as e.g. apt does?

It says ‘run as root’, not installed using root privileges. You’d also need root privilege to dd an image onto a drive either.

Thanks.

For some reason it’s not included in Debian Bookworm (currently stable) and Bullseye. It previously was in Buster and will hopefully again be in Trixie (currently testing).