Hello everyone!
I have added basic cli support to Xpano (Release 0.13.0 - Command line support · krupkat/xpano · GitHub), thank you @robbymilo for the suggestion! It is really basic at the moment (fully automatic, no settings), but it is a start 
If you decide to try it out, please let me know how it works for you / any suggestions for improvement.
Running from flatpak, you will have to add a filesystem permission with Flatseal (it is really easy to do). Example usage from a flatpak:
// Create a 2 image pano with default output name (image1_pano.jpg):
flatpak run cz.krupkat.Xpano image1.jpg image2.jpg
// Launch to gui with all jpgs in the current directory:
flatpak run cz.krupkat.Xpano *.jpg --gui