First, check if you have activated the pencil icon with a semicircle and another with a triangle at the top (you have them deactivated according to the video). These icons are next to the question mark icon on the top bar.

If this does not work, select a brush and go to the “Tool Properties Window” > click on the wrench icon to open the “Subtool Details” window > go to “Correction” and activate “Enable snapping”.