Hamilton stopped on the circuit to pick up the Brazilian flag after taking the chequered flag. There is footage that clearly shows the seatbelt undone as he reached out of his cockpit to get the flag.
Update | Hamilton has been handed a 5,000 euro fine for the incident.
Hamilton to the stewards again
BREAKING: Lewis Hamilton has been summoned to the stewards for undoing his safety belts on the last lap...— ESPN F1 (@ESPNF1) November 14, 2021