There is some foam on the back of the little feet of that OEM silver plate surround. It is possible it’s stuck. FWIW my rear plate is attached with 4 screws....make sure you’ve removed all the screws, then gently yank.
If the screws are removed the plate should move about inside of the frame. If they are both stuck in position, I’d bet a peso you have a screw or two still in. Highly unlikely it would be glued or taped on.
Alternatively, a picture is worth 1000 words.