Discussion of pairing a variety of (old) digital backs with (old) medium format film cameras used to be popular. I wouldn't advise undergoing the pain of trying to do so in 2024 and certainly not as time continues to fugit. Unless, of course you mean a new Hasselblad 907X & CFV 100C outfit, which is brilliant but expensive.
If you want medium format, get a medium format camera. And get your film processed and scanned. My Pentax 645 N was a beast. But I come from a film background and learned to use it long ago when doing so was the mainstream.
Or get a Fuji GFX 100S. (I love mine) Wonderful camera. Absolutely superb lens system. The camera bodies are dirt cheap now that Fuji has come out with their newer models.
Medium format street photography is quite "doable." But I have a real problem with the argument, "I want to use Medium Format because it forces me to slow down and consider each shot and composition, and, and, and."
Anyone can slow down with any camera. Just slow down! Why does it take the camera to make the process go slower? Just slow down and take the care that you would with a slow, big camera.
As for the argument that there is a "medium format look" and that depth of field is shallower with medium format over smaller cameras, just put a good 50mm lens on a full frame camera and shoot at f/1.8 all day (Working slowly, of course).
It'll feel like you're working with MF.
I can show you thousands of images, from Medium Format and Full Frame and you'll only achieve a random chance of identifying which is which. You'll swear the dreamy focus transitions and gorgeous bokeh is from MF, but it will be from FF as often as not.
My Nikon D800E and AF-S Nikkor 50mm at f/2.8-f/1.8 is the best MF camera I've ever shot! (Except for ultimate image quality, which easily goes to the GFX 100S).
Rich