Ok, added another topic. Turns out I wasn’t entirely right that it doesn’t work at all, but still doesn’t look right.
Yes, I tried using classic confinement. I had some issues with this, so I turned back to strict again. Mainly back then it was not supported on all platforms, e.g. Arch (where it should actually work now) and it required an additional flag for installation. Is the latter handled automatically by the software center?
Anyway, for now I have canceled any support for snap packages. It turns out that while Peek itself is a very simple tool, it’s requirements regarding sandboxing aren’t. I don’t have plans to invest any more time into this, I just can’t handle supporting this anymore. I am happy to revisit this once snapd and the surrounding infrastructure have matured a bit more, but it was too much a time sink in the past and the latest results of a Peek snap package where still unsatisfying.
Having said this, the support by various members of the snap team was great.