The explanation of a university stage is that the calculated value is different from the theoretical value because of the ionic activity, because the ionic activity is 1 by default when you calculate, but in fact the ionic activity is not equal to 1. Just upstairs, when the concentration of acetic acid is too high, the difference between ionic activity and 1 is even greater. In fact, there is also a formula for calculating activity, which can be used to calculate the actual activity, thus correcting the calculated pH value, but this formula is a bit complicated, so I won't write it here.