Beginning March 1, 2021, we will remove .NET Core 3.0 from macOS 10.15, Ubuntu 16.04, and Ubuntu 18.04 virtual environments for GitHub-hosted runners. We follow a general guideline of removing software tools from our hosted images six months after they are deprecated, and .NET Core 3.0 reached its end of life on March 3, 2020.

You can continue to use .NET Core 3.0 with our setup-dotnet action. The setup-dotnet action is always the recommended way of using .NET with GitHub Actions because it ensures consistent behavior across different runners or versions of .NET and protects your workflow from possible future deprecation of additional .NET versions:

- uses: actions/checkout@main
- uses: actions/setup-dotnet@v1
    dotnet-version: '3.0.x'
- run: dotnet build <my project>

For the latest updates, be sure to subscribe to the announcement in the actions/virtual-environments repository.