WhatsApp has this frustrating limit of 16 MB or about 1-2 min for videos shared from the camera roll on my iPhone. There seems to be a reasonable workaround through the Google photos app wherein you can use the share option on the video of your choice and select the small option which usually compresses most reasonable length videos so that they can be sent in their entirety on Whatsapp.
The quality is of course pretty poor due to the heavy compression but it’s the simplest workaround.
AB's Reflections 