This happened in Austin, TX. When Uber and Lyft left Austin due to a driver fingerprint ordinance, RideAustin, a local non-profit with the backing of an Austin tech mogul, sprung up. Ride Austin paid drivers better, had a round-up option to support local charities, and though there were some early kinks with the app most of those went away after a couple months. I was a big fan and supported them as much as I could.
The second Uber and Lyft came back (state legislature overrode Austin's ordinance), Ride Austin's ridership plummeted. I tried to still take them whenever I could, but over time it became harder and harder (fewer riders meant fewer quality drivers). After 3 bad pickup experiences at the airport I said forget it. Covid was the final nail in the RideAustin coffin and it closed in June.
Of course California is a much bigger market so any competitors may have better luck, but I still think a lot will be wary if it's just a matter of time before the big boys come back in one form or another.