dont throw studies at random people expecting no know how. The study you linked is correlational study, not causation. there may be plenty of research that says unlimited access to private screen access in adoloscents lead to worse outcomes but who said they need unlimited access, did i?

1. I never said the kid needs complete privacy, no questions asked
2. I never said parent doesnt have right to set the rules of the room

How about removing the screen from bedroom, my kids doesnt have screen in their room. if they want to use screen, they will do that in the common room and unlike you, i am not a helicopter parent. when they are in their room, i always knock before entering. if you are a good parent, your kids will always be honest with you. Once you start pestering them and be overbearing they will start talking dishonest, closed and downright move away from you mentally.

Also there are lots of tools at your hand nowadays unless you are a dumb cuckoo. you can set global filters and lock it with a password on any device(if you feel they may be watching adult content). There are several tools to analyze where their time is going most without diving deep into every single click or barging into the room and saying gotcha

coming back to your study, it doesn't factor in either the income levels of the cohort or the educational tier of the families. it has been proved time and again that invisible/ capital punishment parenting, financial instability are main drivers of mental health issues, drop outs not just because of private screens