Hi,
We would like to let you know that the Microsoft Framework itself has not provided the snap layout and doesn't appear while the mouse hovers in maximize button for a custom window in WPF.
This issue has already been reported in GitHub issues.
GitHub Link: https://github.com/dotnet/wpf/issues/4825
We will update you with details, once we get the solution from GitHub. We appreciate your patience until then.
Regards,
Karthick Arjunan