"Open with" / CLI / Drag-and-drop not working with strict confinement

@baldeuniversel pretty please read (and understand):

before making any such statements again and stirring up false hope of people. There is no way inkscape will fit any of the supported categories from that list or fulfill any of the requirements listed on this page…

Regardless of the above, the three features listed by @mgmax all work for most other strictly confined snaps, so there is something wrong here that will need fixing…