So previously, when you went to get battery information, the screen on time would represent the actual screen on time of your device since your last full charge.
Now, with OneUI 16, in their infinite wisdom, Samsung have decided that the screen on time is calculated based on the usage PER DAY.
This means that this morning, when I unplugged my phone at 100% I already had 1 and a half hours of screen on time from the previous night.
I see no way to change this back to the way it used to be. Great choice Samsung, great choice