I am not on a Linux machine right now so I am not able to give you and detailed advice about how to do to run an AppImage from the terminal.
However from what you describe in your initial post it sounds as if you have not actually managed to make the AppImage executable. This would explain why the system is asking you what you want to use to open the AppImage. Unfortunately the best way that I know to check all this is with the terminal…
OK so I finally figured a way to open the Terminal right in the folder I want it to be in, and then did the chmod thing, and now I am able to launch Krita and FontForge by double-clicking them! MOST EXCELLENT!
Now I’m currently in a trouble with AppImage installation on Ubuntu mate on Banana-Pi. That’s why I revive the topic. Eventhough I have done everything which was mentioned before, I couldnt get any convenient result.
1-) permissions are given in a right way and then allow executing file as a program etc.
2) chmod u+x sampleprogram.AppImage etc. ( even chmod 777 …)
3) System is up to date.
I checked out a lot and some people say it might be related to “fuse” packets but seem to me no sense.