Canon EOS R3 Advanced User's Manual page 436

2.
Press the <
The AF point changes to a tracking frame [
subject for tracking and follows the subject within the screen if it moves.
To cancel tracking, press the <
The tracking frame changes to [
detected, and you can use <
Once tracking begins, the subject is tracked across the entire screen,
regardless of the specified AF area.
The position of AF areas and points when tracking stops after you
press the shutter button halfway or completely corresponds to the
position of the tracking frame during tracking. The position of AF areas
and points when tracking stops during shooting standby corresponds to
the position before tracking.
3.
Take the picture.
> button.
> to choose a subject to focus on.
436
], which locks on to that
> button again.
] when multiple subjects can be