Maybe this doesn’t make sense, but here goes: one thing that puzzles me a little, perhaps only because of my own ignorance, is that for pushing air
downwards (ie VTOL) development efforts have focused almost entirely on what are effectively propellers – one or two big unshielded rotating wings, or sometimes lots of small ones – whereas for pushing air
backwards (runway takeoff), jet propulsion is increasingly the norm, on smaller and smaller aircraft, now down to the VLJ category.
Of course the military have played with jet propulsion to push air downwards, with vectored thrust as in the Harrier, or with lift jets or fans, but
AFAIK they’re few, and vectored-thrust has mostly gone away from VTOL towards improving manoeuvrability of fighters.