A 18yo is not a child, do not to treat him/her as one. The violence of taking stuff away and the lack of conversation, is more problematic than the screen time

A 18yo is not a child, do not to treat him/her as one. The violence of taking stuff away and the lack of conversation, is more problematic than the screen time. Have one (or many) respectful conversations about screen time addiction. Every addictive habit has a feedback loop of "Trigger/Routine/Reward". Talk with her to change some parts of that cycle. For example, instead of watching anime alone, it could be social -in person- activity with friends (same reward, different routine). What is the trigger for these activities? Perhaps this person is depressed, and the depression is the trigger for that routine (even if is not that rewarding). In that case, ask for professional help. Summary. Be creative, patient, and *listen*.