Run this locally - once per setup:
dotnet nuget add source \
--username YOUR_GITHUB_USERNAME \
--password YOUR_PAT_TOKEN \
--store-password-in-clear-text \
--name github \
"https://nuget.pkg.github.com/your-org/index.json"
The PAT needs only read:packages scope for restore. write:packages is only needed if you're pushing manually rather than via CI.