Is the owner of a YouTube channel that teaches girls how to apply nail polish and draw designs sinful for every girl who applies what she learns from her channel, given the owner's intention is to practice her hobby, not to teach girls to attract attention?

The means take the rulings of their ends. That which leads to the forbidden is forbidden, and that without which abstaining from the forbidden is impossible, then abstaining from it becomes obligatory, based on His — the Most High’s — saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." The owner of the channel may not be safe from aiding in evil and guiding towards it. Therefore, he should use the channel for teaching the Qur’an and Islamic sciences to spread goodness.