While there are many distinct subgenres, not all works of fiction fit easily into well defined pigeon holes. To an old school traditional science-fiction buff Unus Solum would be readily embraced as 'science-fiction" without any need for further qualification. It might be described as a "lost-colony" type of story. Though because it has a mainly because a nineteen-seventies cultural ambience, with magnetic levitating airships this could attract an additional label of "retro-futuristic".
On another level it could be alternatively classified as "fantastic adventure" (although this does depend on how much "adventure" there is in this world's fictional content). "Fantastic adventures" are a wide category, but basically they are adventure stories with added fantastic elements which can be science-fictional, supernatural, occult or pseudoscientific in nature. Sometimes this includes mixtures from all departments of the fantastic. Examples of cinematic fantastic adventure are Star Wars and Raiders of the Lost Ark. It is a very broad category.
Because, or so it seems to this author, events of Unus Solum take place on the one planet this might be, yet again, characterized as "planetary romance". Edgar Rice Burroughs" Barsoom series of novels are the principal progenitor of this subgenre.
The simple answer is that the world of Unus Solum doesn't fit easily or readily into any one distinct subgenre. It does fit equally well into the two broad genres of science-fiction and fantastic adventure. It also falls into the subgenres of "lost-colony" stories and "planetary romance". yet overall there seems to be a patina of retro-futurism.
The old-school traditionalist would lean towards science-fiction, but would concede it does well as fantastic adventure. Yes there are clear elements of dieselpunk and cyberpunk, while airships usually connote steampunk, however, magnetically levitated airships aren't in that overheated category.
While it is possible to simply point that Unus Solum has elements of all these genres and subgenres, this doesn't prevent you from creating your own subgenre branding. So you could label it as "retrofuture-punk adventure" and no-one would be able to stop you. Of course, it might be simpler to call it, say, "Exoplanetary Adventure" on the grounds that Unus Solum is an exoplanet. This would avoid worrying about genre and subgenre distinctions. Labels are the least of your worries, just focus on the worldbuilding and the stories that go with it. Always have fun doing so.