Canon EOS R6 Mark II Mirrorless Camera with 24-105mm f/4-7.1 Lens - Manual (Page 553)

3.
Press the shutter button halfway, then release it.
A tracking frame ( ) is displayed if multiple subjects are detected.
4.
Use < > to set your preferred subject.
Either press < > straight in or press it left or right.
The tracking frame changes to [ ] and locks on to that subject for
tracking.
To release locked tracking, press < >.
Caution
[ ] is not displayed on both sides of the frame during Servo AF,
even if multiple subjects are detected.
During Servo AF, it is not possible to switch to a different type of
subject than the one being tracked.
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