Mine is a few years older than yours. We just talk about it and set clear expectations. The only context I allow her to watch videos is when she's video chatting with her grandparents and they co-watch cartoons in another language so she can learn. So I hit a few birds with one stone.

On special occasions we watch movies on the projector.

Consistency is key; don't break the rules yourself. When my wife watches videos at the dinner table my child points out the offense and I happily encourage her to stick to the rules.

Kids let you know when they don't like something. In that case you can try to explain the rationale for the rule at their level. That works for me. Weaving some fun into the rule can make it easier to go down; e.g., making funny faces while you brush your teeth for one minute.

Sometimes they will try to surreptitiously break rules. And you can have a talk about that.