The message and the web site indicated in the message are both a threat
findmy-apps.online does not belong to Apple, despite everything seems to be the original apple page.... but in this case you enter your appleId password and it finishes in the hackers' hands.
REPLACE IMMEDIATELY THE APPLEID passwd on all your devices !!!!!
PS: it is not possible to erase a device that is already supposed to be erased. And after a while it simply disappears from the list of your devices and you cannot longer do anything. I contacted Apple Support and wanted at least give them the serial of the stolen device, in case one day it appears in some Apple Store for intervention..... but it seems a waste of time...