Can't get X11 to work in macOS Big Sur
Solution 1:
This is a common issue since for X Windows you need to run a server process on your Mac and the xeyes client process runs in AWS (or the client program could run locally on your Mac). By default (starting with 10.8 Mountain Lion) macOS doesn’t ship a X11 server so you would need to load and run that for your setup to work.
https://www.xquartz.org/releases/index.html
After installation, you must start XQuartz.app, then ssh -X will start working