Most people don’t really get out their way to set up backup manually. Either system should try really hard to avoid corruption or implement a recovery system. Ideally both.

Just use libdecor. Client is supposed to manage its content.

Packaging software for linux is an insane problem. All distributions are so similar yet so different, all of these nuisances prevent you from making much assumptions about the host OS which for instance forced flatpak to be basically a generic distro you run apps on. For obvious reasons it’s not an ideal situation, memory consumption is bad, performance in various ways is impacted. I believe that the true packaging format will have to cut some corners and be specific by design to smaller set of distributions. Pretty much how snaps are built around Ubuntu, which imo. is a necessary compromise to have something reasonably fast and lightweight.