I think I have a more updated one: install.txt (783.5 KB)
The main story though - Is the pre-R4.0 instructions should be fine on < 4.0 setups. After R 4.0, Rtools40 should be used on windows, and Xcode (only) should be used on osx. Any previous configurations should be stripped out (in .Rprofile, .Renviron, and R/Makevars{.win}). They can be recreated with optimization options only (and the Rstudio parallel fix for OSX); no need for paths.