I've been using RStudio for some weeks now with no problems, but the last 2 days whenever I open the program, it is stuck on this loading screen. After a while, a pop-up message comes up saying that "The RStudio server takes a long time to respond."
My R version is 3.6.1 and RStudio is 1.2.5019. I added it on the firewall exceptions, I tried to reinstall R and RStudio.
Try changing to software rendering, you can change it by holding the Ctrl key while opening RStudio, then you should see this menu and change the "Rendering Engine" to "Software".
It's possible that R / RStudio is hanging while attempting to load an old (very large?) R workspace, or while attempting to render an old R Markdown notebook with a large amount of inline output.