Slide a drywall knife between the wall and metal. You're going to screw up the drywall, just not too badly.

Take the glass out and lift up on frame it may have screws holding it up from behind.

@Joseph Corlett, LLC thank you

Sledgehammer. Kidding. Maybe they glued the glass in?

I’d still try gently pushing it straight up on the frame part even with the glass in place.

@ShadyWillowFarm sledgehammer sounds the most fun

I pushed the glass to the side a little bit and it revealed a screw between the frame and the glass. It appears the glass may be held in place by 4 rectangular pieces. Two on each side. I’ve attached pictures.

A bit disappointed that you didn’t get the sledgehammer out…