Not experiencing lag either,will be somewhat frustrating for those who have this issue though. For those with issues like @sarasphotobox best to send an error report via Samsung Members. Lower CPU speed may cause lag though. Could try Factory Reset (ensuring Data is backed up beforehand).
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.
"Power Saving mode", will limit your screen refresh rate to 60Hz and reduce your CPU speed to 70% and will cause lags.