In finland taxi drivers are regular salaried workers earning hourly wage during working hours regardless if they have customers or not and they may earn additionally provision of sales. Caveat here is that some taxies are self-employed which makes the situation bit more complicated
uh, pay them a monthly wage for doing 9-5 and the drivers would drive as much or as less, what the app makes them work
The question stands: are there any taxi-like systems that work like that? Traditional taxies certainly did not employ their drivers and pay them a wage, they were still very much working for their fares.
Hired cars sometimes pay their employees that way (the driver gets $/hr no matter what), hence you have to schedule well in advance.