If you review Step 8 in this Teardown of the Watch you’ll see the pictured part is not the ForceTouch sensor Apple Watch Series 4 Teardown
As to what it is would be tough as there is not enough information in the image to gain a sense of scale or understanding the parts construction.
Using the teardown can you see what it is.
@ebp049x - OK, was out enjoying the day sorry for not piping up sooner.
The display assembly is made up of a collection of discrete elements the crystal glass, the touch plate, the OLED screen, the backplate which holds the NFC chip.
What I see is a bunch of mangled parts and you still have part of the display assembly attached to the watches body.
You will need to get a new display assembly to fix this. Here’s the guide which also has the parts info Apple Watch Series 4 Screen Replacement
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