@Graham37 We really should not have SD channels in this day and age, however that is another matter. In the past though of course were happy enough. Generally Movie or standard the best option, could experiment with Settings but unlikely to make much difference. May not be particularly relevant to this issue but Auto Motion Plus in most cases should be kept to Minimum or switched off. Not sure if you use 4K/HDR but according to Rtings does not get very bright in this model and cannot display a wide colour gamut.
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 5.0,Android 13 .