This is older analysis [1] but Uber is profitable on each ride in their biggest markets until you deduct the OPEX of the main co. The burn of sales, marketing, engineering, support, their rider safety team, the driver inspection and on boarding centers, leases, etc all continue on with or without riders.

[1] https://benjamintseng.com/2019/04/lyft-vs-uber-a-tale-of-two...