But that's what is weird. It's really a basic appimage, no plugins.
I followed the instructions, I didn't install any plugin, I even tried to extract and open the appimage from a X11 session, I indeed have the same error message you received either because of Wayland or because of plugins, but it's an error message I receive by default, whatever I'm trying... ='(
I suppose maybe something, like a package I installed is not compatible with the software, or there is something else happening on my PC, and maybe reinstalling Solus would fix that, but I don't wish to do it. I already set up all my OS, all my DE settings, all my softwares, everything works PERFECTLY... except for that ONE software, and I don't understand why.