To prevent RStudio from hanging when GitHub copilot was in use, I switched off automated copilot completions by going here in RStudio:

Tools --> Global Options --> Copilot

Then, I left Enable GitHub copilot ticked, but switched Show Copilot code suggestions from Automatically to Manually (Ctrl + Backslash).

This means that whenever I want to use completions, I can just press Ctrl + Backslash after the comment/ instruction / piece of code.