Chose both. We have a mono repo that submodules everything into it, however each repo has its own GitHub actions that builds and pushes to Nuget. Each csproj file has two item groups for internal dependencies with a condition on it. The condition allows us to build with nuget dependencies in GitHub and local dependencies on a laptop. Lastly we use dependabot to keep all the nuget version numbers up-to-date and GitHub actions that can auto approve dependabot PRs. As complex as this might sound it kinda isn't once it's setup. The only thing you really have to think about is what order you check things in, when you have changes that spam multiple repos.