There isn't a simple answer to this, and in most cases, the only accurate thing to be recorded is boarding point (and that can vary if some or all forms of non-cash ticket require drivers to press a button to record it, as driver compliance will vary.) Where tickets are smartcard or involve a QR code, then the type of ticket will be recorded fully, relying on drivers to press different combinations of button for each type of ticket will have some degree of inaccuracy.
Even where a non cash transaction (return tickets, day or longer tickets, concession passes) is recorded by a machine, or where there's a flat / zone fare scheme, the machine won't know where that passenger is getting off. Some earlier generations of electronic ticket machine (ETM) would record an alighting point for non-cash journeys, but this could either be the final point on the route, or the point where the most recent cash ticket was issued to.
To an extent, you can take boardings in one direction and assume that an equivalent number of people will get off at the equivalent stop in the opposite direction - there may be some cases where this is more accurate than others, and doesn't give detail in terms of time of day.
Not all operators want to pay ETM providers for add-ons, and I'd expect that driver compliance with recording alighting passengers is going to be even less reliable than their recording of boarding passengers - especially at the few operators who still have centre exit buses. In theory, an operator can compare figures recorded by each driver and 'have words' with drivers whose figures are consistently well outside the average, but not sure how many operators have the office staff resources to do this, or the desire to 'carpet' drivers for minor things while there's a significant driver shortage across much of the industry.
I've not had any experience of cameras near the door/s being used for this, or of operators trawling through CCTV for origin + destination information.
