See my first reply to you. You said that it is not the same as your wife's but the same as your friend.
O2U is the CSC code for the U.K. carrier branded firmware for the O2 network
Android 11 has not been released for this CSC code to-date.
Same model number and CSC code?
Well, there is your answer then. You do not have the same CSC codes and are running different firmware.
On the Galaxy S20, it took 2 weeks before O2 certified their Android 11 firmware release.