It’s plausible that city could be grown in space as a vacuum is a good environment for spores and their makeup benefits greatly for space itself. Although it’s an enclosed system they have randomly grown in the iss before. If they can fruit then there’s mycelium and that’s what’s been used as a building material on earth already.

I read an article years ago about how they could colonize star systems in xx amount of years.

Here’s what I found w a quick google search on the subject

https://www.zamnesia.com/blog-the-mushroom-our-extraterrestrial-friend-from-outer-space-n653