The crash is not related to the entities package or even Unity. If I am commenting the call to open the file dialog in the class ImageToTiles.ReadTexture(), there is no issue. It is most likely coming from the Windows API being used to open the dialog (https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.openfiledialog?view=windowsdesktop-9.0).
The stack trace of the crash is referring to some windows API.