The "Exec" field in /usr/local/share/applications/me.mitya57.ReText.desktop is set to "retext %F". I believe that it should be set to something like "retext.py %F" instead. Otherwise, a user may not start the program from a desktop menu.
I think the right fix would be to create bin/retext
It was removed by yuri's change I think.
A commit references this bug:
Date: Mon Feb 11 21:14:32 UTC 2019
New revision: 492737
Update to a snapshot from master.
This should fix the wrong desktop file entry.
Add missing dependencies while here
Reported by: 0mp
Obtained from: https://github.com/retext-project/retext/issues/425
Thanks for your report. The issue should be fixed now.