X11 is not available in R

The XQuartz package is the Mac X11 and your version is the current one. I'm wondering if you need to reboot after installation although I don't claim to know that. (And it might not hurt to repair permissions.) On my Mac (running 3.3.0 on El Cap) I need to set width and height (in inches, not pixels or points);

 x11( width=3, height=3)

What do you get with:

Sys.getenv("DISPLAY")

Might be something along the lines of:

"/private/tmp/com.apple.launchd.KImNTikz8K/org.macosforge.xquartz:0"

Also run:

capabilities()

I had this same issue and installing R separately from Rstudio fixed it. You can download it from here and verify x11 is working using x11()

You have to have a local X server, so get XQuartz because you are on MacOS.

If you were on Ubuntu you could install the virtual framebuffer X11 server like said here:

apt-get install xvfb xauth xfonts-base

Now that you have X virtual framebuffer installed, you can start a new instance like said here:

Xvfb :0 -ac -screen 0 1960x2000x24 &

Then if your R is compiled with with-x configuration option (enabled by default), you should have X11 capability, and you just have to declare this in R:

Sys.setenv("DISPLAY"=":0")