how can I change the .NET to .NET Framework 4.7.2 i am really struggeling since 2 days now. I am doing a WinFormApp and can only use .NET 5 or .NET Core 3.1 but i need .NET Framework 4.7.2 for another Framework. Already installed it through [Microsoft] but it dont appear there to select.
Well, as your main application is .NET Core, it's running on a core CLR. It cannot be changed to a non-core CLR project. You would need to restart a project if there is no way of achieving the goal you need.
If you also need the .NET Core application for whatever reason, I would recommend using an API call to communicate between the two applications or another method of communication which isn't with the project itself.