Have you ever seen a config where somebody made the minibuffer pop in center of the screen? Perhabs by creating a temp screen

Yes. It's done with posframe or other packages like that

If you use vertico there are a few options to do this

It's on their readme

I see cool

Question for nix users, how would you run a process from nix env in a project in an already running emacs? Let's say my nix env defines the java version, how would you wire these things together?