I don't know if this is still true, but a few years ago Uber was losing money on every trip [1]. They also, five years ago, had 6000 employees, of which 2000 were engineers [2]. Apologies for the outdated links, there's probably more precise data out there.
I read the top article, it’s good. The pertinent bit to my question seems to be, they do subsidise drivers. Apart from fixed costs, they have “driver incentives” to shape supply and demand. Ie give out cash to subsidise trips when needed.