Hello!
I have the same problem, so I did that, but does not work .
install.packages("xfun")
Yesterday I was able to knit the R Markdown code into PDF documents without problems, and suddenly is not possible anymore. I get the same error message:
Fehler in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]) :
namespace 'xfun' 0.16 is already loaded, but >= 0.19 is required
Ruft auf: <Anonymous> ... namespaceImportFrom -> asNamespace -> loadNamespace
Thanks in advance!