GTA 4 had real taxi mechanics. GTA V had taxis as scenery. GTA 6 is contemporary - ride-hailing is plausible.
Visible in trailers
Taxis in traffic. No specific ride-hailing branded vehicles visible (Rockstar would invent fictional brands anyway).
Taxis have been in GTA. Whether ride-hailing is part of GTA 6 is the new question.
GTA 4 had real taxi mechanics. GTA V had taxis as scenery. GTA 6 is contemporary - ride-hailing is plausible.
Taxis in traffic. No specific ride-hailing branded vehicles visible (Rockstar would invent fictional brands anyway).
Speculative. Plausible given the contemporary setting.