UNMAINTAINED! PLEASE SEE @MangriMen's fork
Right click in any .mgcb file to open it in the MonoGame Content Builder editor.
Install and set up the MGCB Editor. If you have dotnet installed:
dotnet tool install --global dotnet-mgcb-editor
mgcb-editor --register
Note: If you are using the older versions of the editor, then you need to update its path in the project's setting accordingly.