Kattegat where I live is probably double the width of Hormuz and if you're in a small ship you can probably sail most of those 140 km. Not without risk, but you'd be relatively safe for the most part. Big ships can't though, so even though there might be 50km on each side of them they could potentially have a shipping lane which is only a few hundred meters wide.

I can't say that I know anything about Iran, but if we were to close our straits off so you couldn't enter the north sea from the baltic sea then our navy would rapidly deploy various different mines that lay on the bottom on the shallower parts and control the shipping lanes with things like suicide drones. I imagine Iran would do something similar, only they've probably been preparing for it a lot more than we have.