Is there a solution when using Microsoft.WinForms.Designer.SDK and Reflection in your Project?

Okay, so using Microsoft.WinForms.Designer.SDK solved it for me, but required one more change to the codebase.

And for future searchers and finders of this topic:
While the Assembly containing the System.Windows.Forms.Design.ParentControlDesigner is available during runtime, the assembly that contains Microsoft.DotNet.DesignTools.Designers.ParentControlDesigner is not.

This means, that Reflection that resolves all included Type-dependencies ( like Assembly.GetTypes() ) on the assembly that contains the designer-class will now lead to a "file not found" exception during runtime.

_Originally posted by @CortiWins in https://github.com/dotnet/winforms/issues/11531#issuecomment-2169282036_