Damaged iMac Display - Any Solution for Grey Vertical Column Lines?
Yes. Unfortunately, you damaged the display.
If seen this exact problem (different size and location of the bar) and it was due to a “hit” to the display along the edge of the glass.
These LCD panels are few and far between now in terms of availability. You may be able to source it used via eBay or find an iMac “for parts” that hopefully has a good LCD. Your other option would be to get a new(er) model And sell that as parts to help fund the replacement
Can you modify the display?  Unfortunately no. The screen is still reporting that it’s 2560 pixels wide (EDID data). It’s hard coded into the firmware so you can’t override it to trick macOS that it’s smaller and render the display output so it “bypasses” the defective part.