I'm not as familiar with the R installation on Mac. Is the installation portable? (ie can the contents of the R folder in "Applications" be transferred to another computer and not have issues?)
Unfortunately it seems like it might not be, but I would love to hear if there might a workaround to try.
If you update your macOS version, you should re-install R (and perhaps XQuartz): the installer may tailor the installation to the current version of the OS.