there is a blog post with some details about it here:
github.blog/news-insights/comp…
specifically:

"This program does not use:

• Interaction data from Copilot Business, Copilot Enterprise, or enterprise-owned repositories
• Interaction data from users who opt out of model training in their Copilot settings
• Content from your issues, discussions, or private repositories at rest. We use the phrase “at rest” deliberately because Copilot does process code from private repositories when you are actively using Copilot. This interaction data is required to run the service and could be used for model training unless you opt out.

(emphasis mine..)

Updates to GitHub Copilot interaction data usage policy - The GitHub Blog

From April 24 onward, interaction data from Copilot Free, Pro, and Pro+ users will be used to train and improve our AI models unless they opt out.

^{Mario Rodriguez (The GitHub Blog)}