I noticed that Minder crashes as soon as you saved/ serialized your first mindmap to a file.
Here is what the console outputs when you open Minder again:
~ >>> com.github.phase1geo.minder  I/O warning : failed to load external entity "/home/laurenz/.local/share/minder/favorites.xml" I/O warning : failed to load external entity "/home/laurenz/.local/share/minder/exports.xml" free(): invalid pointer zsh: abort (core dumped) com.github.phase1geo.minder
It is irrelevant if you open Minder via the launcher or by opening a saved file.
You can delete the config directory in “~/.local/share/minder” which makes it at least possible to open Minder again, but you still cannot open your saved mindmap.
I am using the latest Manjaro under Gnome.