Unfortunately whilst your snap may have a requirement to use classic confinement (ie the ability to access and modify arbitrary files on the host system), I am not sure it fits within one of the supported categories - can you please refer to Process for reviewing classic confinement snaps and help me understand if it does fit within one of the existing categories?
Also from the general discription of the app at https://github.com/funbiscuit/spacedisplay it seems like it is more focussed on just needing read access rather than write - in which case, I expect the majority of the usecases for this snap would be met via strict confinement with system-backup
and mount-observe
.