God......its almost impossible to make a close recommendation with no budget.
Forget about lens comparisons with 35mm cameras, there isn't the range or availability that there is for 35mm, a 20mm equivalent on MF is the fishiest fisheyed thing you'll ever see, its gettable with some systems but pretty niche tbh.
50mm is plenty wide enough.
No square ?.....well 645 has a lot of followers.
To keep it simple, a fixed lens Fuji 645 RF.
Something with a few more options, Mamiya 645 has a sweet easy to get 45mm, or Bronica ETRs
The RB/RZ is 6x7, I don't feel its worth the extra weight for 10mm of extra film over a 6x6, but theres plenty of them, they're cheap and available.
There are lots of other possibilities but a team of a hundred trained monkeys typing for 3 weeks night and day, could not list them all without a budget to narrow things down a bit.