Hi,
I just got the same message after updating my 2024 iPad pro 13 to iOS18.
Checking the info section of the iPad settings, I found this wrong status as well, saying the display is not an original Apple display.
I bought this iPad at Apple and not via a third party shop, so the display must be an original Apple part.
After a restart, this status in the info section was no longer shown.
Anyway I am a little bit confused and not sure, if the iOS18 software manages the display correctly, i.e. in terms of HDR and brightness control?
Hope this will be sorted out by Apple soon.