You can go to phone Settings > Additional/System settings > Developer options > OEM (Original Equipment Manufacturer) unlocking to see if the OEM unlocking menu is grayed out.
(If the OEM unlock menu is gray, it means it has been unlocked. If the OEM unlock menu can be opened or closed normally, it will be in the locked state.)
Note: If the developer mode is not displayed in Settings > Additional settings, you can turn on the developer mode in Settings > About phone > click the version number 7 times in a row.