The same thing happens to me (see attached images).
In pgAdmin4 v5.1 (Windows 10 enterprise) it's a blank screen. In pgAdmin4 v5.2 (Windows 10 pro) it's looks like it's stuck on the loading screen (but it's already finished loading).
I can reproduce this all day, when I am connecting via an RDP connection (which is how I typically connect). When I go to the same windows machine directly (Windows 10 pro is a physical machine, Windows 10 enterprise is a remote virtual machine) the behavior isn't replicated. The application opens as expected. I suspect it isn't redrawing, or letting the underlying operating system know to invalidate the window when it's done loading in a manner that RDP knows it needs to redraw the window. The local display seems to be smart enough to accommodate for this oversight. I hope that helps.
rik.
[I've updated the bug report, I'm just repeating myself here for those that are curious but don't follow RedMine]
