No, you can also have a mini roundabout, which is a white circle painted on the road. Maybe slightly raised but with no kerb so you can just drive over it. Yield to anybody in the junction and yield to the right (we drive on the left).

Very common in the UK instead of stop signs at intersections. Stop signs are only in rare places where a hedge or other environment prevents you from being able to see and yield to approaching traffic while approaching the junction. Even in that case there would never be a four way stop.

Interesting. We have a few of those in the US, but get this, they have stop signs too!

IIRC Vigo, in Galicia (Spain) struck me as a case of a decently dense city that used roundabouts at relatively compact intersections in the city center, along one street at least: https://maps.app.goo.gl/CwZYypxT5SjBr1QE7?g_st=ic

even it it were the case, it's not like American roads lack in space

They do in some places, like SF. Though even SF has more road than some Europe or Middle East cities.