IIRC from when I first read this back in 2020, it's Lyft. The hint is at the end (emphasis mine):

"In retrospect, there were many red flags. *Well, pink flags.* Whatever."

Does Lyft have pink flags or something? I don't get the significance.

(I've never used Lyft or Uber in my life though, so maybe that's why)

Give "Lyft color scheme" a quick search :)

EDIT: Okay, I see you added an edit where you say you've never used it - so to remove any semblance of snark I'll clarify that you will in fact find pink if you do that.

I see, thanks!