David wrote:

I can see the metal plate flexing out with the broken bit of the back; I
assume that it is bonded to the plastic of the back.

The only other option I can visualise would be for there to be a metal
chassis for the whole TV which I don't thing is likely these days.

Maybe a brass bush pressed into a supposedly solid part of the plastic
case and the VESA screws go through into it? If it's been bouncing down
the road they could have worked loose - epoxy?