I tend to have a general idea, nothing too specific unless I use a real-world reference (which even then, I subconsciously blur out whatever's not mandatory to know about). General streets, buildings, rooms, planted trees, faceless uninteresting crowds in the background.. Stuff like that is purely visual and filtered for practical use.
And in terms of characters interacting, I'd say that's the most vivid part of the writing experience as I prefer to act things out and smooth out dialogue before permanently adding it to script. Emotions and physical sensations are felt out as well.. To the best of my ability, anyways. There's a lot of grave injuries in there that I've never felt and could never possibly just imagine feeling lmao
In short, my mind's eye sees everything like you would for directing a film and comes with the same limitations. Characters matter infinitely more than everything else going on for my process lol