See Chris’answer at question 94697:
“I think this is what you’re looking for: https://appstore.home.mendix.com/link/app/78474/
Or maybe this one: https://appstore.home.mendix.com/link/app/21721/”
One thing you could try is the Exit Intent widget. This will show a message if a user tries to re-load or leave a page with unsaved data.