No, cpu wise there should not really be an overhead, as it just uses docker or podman to run the application in question. the only bottleneck i see could be host filesystems that are not supported by docker/podman and therefore could lead to slow file access in the container.

In the end you could use any distro which desktop you like (which could be Debian stable, or something immutable) and then get your applications from the latest and greatest with Distrobox

If you like web tools maybe https://github.com/Frooodle/Stirling-PDF could be something for you.

Congrats on the impressive 0.0.1 version. The one thing that I was missing in Mlem, that is also not part of this app is ipados support.

Another +1 for restic. To simplify the backup I am however using https://autorestic.vercel.app/, which is triggered from systemd timers for automated backups.