Canon EOS REBEL T6 (W) Mode D'emploi De Base page 67

During Live View shooting, it may be difficult to focus on dots of light such as
in a night scene. In such a case, it is recommended that you set the AF
method to [Quick mode] and shoot. If it is still difficult to focus, set the lens's
focus mode switch to <MF> and focus manually.
Tell the subject to keep still even after the flash fires.

If you use the self-timer together with flash, the self-timer lamp will light

up briefly after the picture is taken.
6 Shooting Night Portraits
65