I’m working on a late 2018 macbook pro (6-core i7, Intel UHD Graphics 630 and Radeon Pro 560X graphics cards, 2tb ssd), running rhino v. 6.18.19249.01112, 2019-09-06
Modeling in general, but especially the layouts view, is unbearably slow on an external display (like 0.5-1fps slow, totally unworkable). I found this unsanswered thread that made some difference – keeping all detail views in wireframe helps slightly – but it’s still pretty rough. It’s noticeable, but less bad, on the internal display.
Doing the same thing to the same model works fine in rhino 5, but it sucks to be constantly exporting back and forth.