Dag @FrederikP: There have been problems with the CRAN repositiories for MAC updating correctly, so I would recommend opening the R app (not RStudio) directly, and running install.packages(), with no arguments. That will create an interactive call which allows you to pick 1) where you'd like to get your packages from, and 2) which package you'd like to install. Some locations are fine, and others aren't, but it's not clear which, so I would recommend starting with ones close by (Ghent), and seeing what works.