First of all, Apple had great innovation. But this sucks major balls.
I would pull a DIY repair video. You know it is a 27' 5k display, so get it out of the LG monitor and make it fit hey.
I don't know if it is a option but go to another Apple store. Or just get another broken one. Use those parts and biperdibaperdyboop, Imac fixed. Cause if Apple is like this to more People, those people are going to sell their Imacs.