I have the same issue: MGBA roms are recognized correctly, but in NESTOPIA can´t see any extensions (no zip and no nes) after edit the “action.config” the issue persist. No files recognized in the folder 
Show us your action.config file.
Finally I can fix it, but is strange because the problem is,when I open the file of the configuration with “notepad” in windows, I made some modifications and then I saved them… I saw that it did not work and I rewrote it exactly as it was originally (because I had a backup file) but is not works!
So, I think if you open any configuration file with the windows notepad, you see the texts are stuck together, and then you leave everything as it was, you have really modified the lines and it does not work. You have to make separations even if you see in the original file that they are together and working fine.
In the moment that you touch the text file with the notepad, there is not the same, and you have problems then.
It sucks to work from windows.
Hi Guys
how do i create a file called action.config with my IMAc?
I assume you to create a normal ‘.txt-File’ and editing the extension snippet to ‘.config’ if you’re done.
You can use the stock text editor for this. Just duplicate a action.config from the game shell. Open it with text editor. And configure it the way you want.
You can also add ‘zip’ to the MGBA in the same manner.
If you are ssh’ing in use nano
nano action.config
That will create the file. Whatever you do be careful that it is an absolutely basic text file. Lots of little formatting things can cause issues.