La fonction de suggestion automatique permet d'affiner rapidement votre recherche en suggérant des correspondances possibles au fur et à mesure de la frappe.
I tested in my end and was able to confirm that while creating a new property it is not expected to receive a warning message while clicking X or close. You will need to ensure you have your property data saved before creating the new property so no data is lost.
However, I do think it is a great idea.
My recommendation would be to please post your idea in our Ideas forum here, where it's currently watched by our development team, and any new idea that receives more votes the more impact it has on HubSpot’s product development.
Confirmation dialog: When a user attempts to close the window with unsaved changes, display a confirmation dialog box asking for confirmation before closing. The dialog can provide options such as "Save and Close," "Discard Changes and Close," or "Cancel" to allow the user to take the desired action. This gives them the opportunity to save their changes or cancel the closing process.