How to start application with GUI?

Kodi runs as a GLES app directly on the framebuffer, no Windowing system. I'll also caution that mono support is an endangered species because it's a major pain in the butt to cross-compile (automated builds fail regularly) and we're in the process of reconfiguring add-ons that depend on it to use .net core which is lighter and easier to work with. Once that's done the current mono add-on will be removed from our add-on repo. To add extra incentive; our current (limited) support for .net things has been tested solely with the couple of add-ons that use it, so we couldn't comment on what support there is for your unknown application.