Just to clarify, RStudio (which is just an IDE for the R programming language) has nothing to do with your R package library, your problem was that after a major R update, you need to update (which actually reinstalls) your packages so they get compiled for the current version, usually you do this by running this command:
When a new major version of R is installed in MacOS, a new folder for packages is created in the user's Library. That folder is empty, which means that your User Library in Rstudio is empty. I usually just install all my packages anew from the latest CRAN repo, which can be time consuming but seems to be the safest way. Given that SFdude had no problems when running R outside of RStudio, this is what I assumed he had done. Have you had a good outcome from copying the packages from the old library folder to the new one and running update.packages(), or is there a better way?
You could even rename the folder or point your package library to the old location using the R_LIBS_SITE environmental variable but after a major R version update update.packages(checkBuilt = TRUE) is going to reinstall everything anyways because all packages require recompiling.
Is not my intention to antagonize you but this comment can be misleading to other people reading it. as I said before, RStudio is just an IDE for the R programming language, the version you are using doesn't affect your R package library, it's compatibility with an specific R version is a different matter.
