Saw a review the JetBrains page that Rider isn't officially supported, but they ...

kesslern · on Oct 27, 2021

Looks like I can download it from the plugin page and manually install the zip file. Thanks!

https://plugins.jetbrains.com/plugin/17718-github-copilot/ve...

EDIT: Hmm, it installed but it refuses to run.

EDIT2: Looks like you can force the plugin to work by editing the plugin.xml contained in github-copilot-intellij-1.0.1.jar within the plugin archive. Just remove the line that includes Rider as incompatible. The same should work for CLion.