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.
Where did you purchase your phone? reason i ask is because many stuck on such an old version have bought them from places like eBay and amazon and they were USA or other country imports (grey imports) and wont update unless sent back to that country to update.