Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 543)

543
HDMI Output Resolution
Set the image output resolution used when the camera is connected to a
television or external recording device with an HDMI cable.
1 Select [ 5 : HDMI resolution].
2 Select an item.
 Auto
The images will automatically be
displayed at the optimum resolution
matching the connected television.
 1080p
Output at 1080p resolution. Select if you
prefer to avoid display or delay issues
when the camera switches resolution.