I cannot find timer on iphone13 camera

Tap  at the top of the Camera screen, tap , choose 3s or 10s, then tap the Shutter button to start the timer.

Do note, only when the camera is set to Photo or Portrait will there be a timer Option.

If set to Video, Time Lapse, Slow Mow or Pano, there is no timer option due to the nature of those modes.

After opening the camera app, you should tap the clock icon at the bottom of the screen, then choose the timer mode.