Unable to install rmarkdown under Windows due to failure to install tinytex

The small part of the error message you are showing is asking you to update the xfun package

install.packages("xfun")

Also, you are using a very old R version so you are going to be forced to install packages from source, which requires compilation and it is much more prone to installation problems. I would strongly recommend updating your R version.

If this doesn't solve your problem, please post the complete error message you get as formatted code (screenshots are considered a bad practice here).