I was looking around for an answer to this and couldn't see to find one for the new One UI 3. But as I was playing around with some of the settings on the S21, I was able to find the Android 11 Easter egg after you enable it from the software version!
This is hidden in the devices button under the quick tools tiles. Once in there, tap the 3 dots and then tap manage apps. You'll be able to turn on the little cat mini game if you are interested in doing so!
