Canon EOS REBEL T8i Advanced User's Manual page 542

Caution
Movie recording continues if the camera is disconnected from Wi-Fi during remote
movie recording.
With a Wi-Fi connection to a smartphone established, certain functions are
unavailable.
In remote shooting, the AF speed may become slower.
Depending on the communication status, image display or shutter release timing
may be delayed.
When saving images to a smartphone, you cannot take a picture even if you press
the camera's shutter button. Also, the camera screen may turn off.
Note
With a Wi-Fi connection established, disabling the smartphone's power saving
function is recommended.
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