I have RStudio 1.3.1073. This is the latest one allowed by my organisation.
I have been used R 3.6.3 but decided to update R.
I did this in the R 3.6.3 console, using installr::updateR() to install R 4.1.0. It hung on the package update step which seems to have introduced a nasty bug.
I was able to update most packages in RStudio (except those that require a newer version of RTools), but now the Plot Pane is not compatible with that version of R and I am getting a pop-out plot window instead. I have not been able to fix this since I can't update RStudio.
Also the Help pane shows URL '/help/doc/html/all.available.html' not found
Reverting to 3.6.3, now when I load my project I get an error box: "rsession.exe - Entry Point Not Found" The procedure entry point R_removeVarFromFrame could not be located in the dynamic link library...
I have RTools 3.5 installed as later versions don't work for me. With rstan mostly.
Now I have rolled back to R 3.6.3 and RStudio won't start due to a rsession.exe error.
Looks like a complete reinstall of R 3.6.3 is the next step.
Update: It looks like that worked.