Problem Description:
Use Unity2018 to create a new project, create a new script, and report an error: The following file: ..\project.sln was executed in the command line. If these files cannot be found, they will not be loaded.
the reason:
See if the project uses Visual Studio 2017 or Visual Studio 2019. Starting from Unity 2018, Visual Studio 2018 is no longer supported. To solve this problem, you can download the VS2017 or VS2019 version, or download VSCode for Unity development.