When you sign in with email, Google, or X we store the name and address those services share, plus the titles you like, save, and resume. That library is scoped to your account and is not sold.
Playback volume and brightness live only on this device. We do not read your phone's hardware brightness or microphone. Progress is saved so Continue Watching works on the next visit.
Sign out from the profile chip in the header. That ends the session on this browser. For questions about your data, write to the address on your account screen.