My current bike has no motor and uses a Gates CDX belt drive with a Shimano 8-gears internal gear hub
I believe thats enough, more gears are not needed
my older chain bike had a motor and I could just let the motor do the work if my chain got too rusty/dirty which resulted in higher wear (loose chain)
the Shimano Alfine 8 has 3 gears below the direct drive (I think what that is called? the one similar to a single speed no gears system) which is pretty ok for most hills
interestingly enough the gear translation on the higher gears is quite steep
while I cruise roughly 18 km/h on the direct drive gear, the next higher one already is more like 22-23 km/h
the more expensive Shimano Alfine 11 has 4 gears below the direct drive gear and the higher ones are still steep increases but slightly less
No idea about cheaper internal gears hubs or other brands though