Hi @Rob99 The Z Fold 3 is expected to receive the One UI 4.0 Android 12 update this month. see some information here: https://9to5google.com/2021/12/03/samsung-android-12-update-rollout/
Anyway glad you are happy with the new software on the S21 Ultra.
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 4.0,Android 12 Official Version.