System is Linux Mint 21.1 , Kicad version 7.0.0 via Flatpack
There was a question back in April of this year but it looks unresolved, and was closed. Today, I had reason to use the text editor, because I had opened a Project that was built in an older version of KiCad (v5.xx), and there were ‘rescued’ schematic symbols; after the rescue, I wanted to open the various symbols and “Save As” to my custom symbols directory on this particular machine. It balked: said I didn’t have my text editor specified.
So just like the prior user (in April), I merrily went away to correct choose / specify that in the Preferences section.
In the Preferences, if you click on the folder symbol, it opens a file-manager window that looks like the one in Nautilus. But Nautilus is NOT my default file manager, it’s Nemo. AND…it sorts / filters the available files in the folders so that only the “Executable(*)” entities are shown. This file manager – which appears to be hard-wired within KiCad — seems blissfullly unaware that Linux programs are not tagged as .exe files. It doesn’t show any files that would normally be tagged as ‘programs’ in Nemo. So there is something peculiar there or, at least it seems so. I also would point out that there appears to be a drop-down menu in the field displaying Executable file() (i.e., it has a down-arrow), BUT, there are no drop-down options.