[markhahn]

but are those details fabricated on demand?

I don't have any trouble following your path of increased detail, but if someone says "imagine an apple", I get a vaguely apple-shaped, generally redish object (I like cosmic crisp), which only becomes detailed if I "navigate my mental eye" closer.

[hosh]

I think that is pretty normal while dreaming, daydreaming, or awake if you don't have aphantasia. Someone skilled in neural-linguistic programming can guide someone into developing greater and greater details.

Psychedelics and certain meditative practices can enhance this effect. There are also specific practices that allow imagined object to take a life of its own.

That's in the private imaginative mindspace. There are other mindspaces. There was one particular dream where I can tell, it was procedurally generated on-demand. When I deliberately took an unusual turn, the entire realm stuttered as whole new areas got procedurally generated. There were other spaces where it was not like that.