OnGUI optimizations, or do I really need to redo it all?

The game's UI relies a lot on OnGUI, not one loop with 100 same items, no, many different GetStyles layered on top of each other.
Nothing uses GUILayout off course and guilayout=false where it matters, but that was back in 4.7, 6 years old stuff.
So I was wondering what optimizations you guys use and also if something substantial was done in more recent version of unity to speed up ongui at runtime. (more recent than 2017 to which I already ported the beast)

 

I'm also interested in this as GUI is pretty slow. Even the scene view spends more time drawing the GUI than the whole scene in my case.