Two cameras checked and “fixed”:

Hasselblad film back was somehow jammed, problem solved by reading and handling more carefully (note to self: dark slide likes to be fully inserted and slow film rewiding is also appreciated, so obvious :/ )

Flexaret checked for rewinding and exposure times as well, as ever since minor repair the shutter was so quiet I hardly believed it fired

and!

I might have just devised a way how to feed it with 220 film, depending on the leakiness of the back.

Otherwise there is no reason for it not to work this way.

Little engineering and one ruined exposed film fixed this all. Hello, two lens world!