A recent Ultimaker Cura update (Cura 5.2) and recent firmware update have had an unexpected message appear on screen, indicating that an Unknown Build Plate Type is being used. This message only appears when printing via USB.
This message will not prevent you from printing. Simply X out of it, and you can continue printing without issue.
Ultimaker is aware of this issue and will fix it in a future firmware update. In the meantime, you can X out of the message when it appears, or downgrade to an older Cura version and the message will not appear. Previous versions of Cura can be found on the Github here.