How to help my pc game addicted child?

I used to play video games a lot, but was older than your DD and mostly played single player games so it was a safe environment.

I wouldn't take her devices or impose sudden drastic measures, I think my approach would be to show interest in her games and youtube videos (and assess safety and appropriateness of content whilst doing so), play some of the games with her and then talk about the games, take an interest like you would in any other hobby.
At the same time I'd start offering alternatives to spending her time and try and gradually and naturally reduce the gaming time.

As others have said, first step is to remove devices. Our DC have very controlled screen time. I think most adults know how bloody addictive these things are!

clear your heads not lear yur heads

I agree. Cut them off entirely but explain to her why. Not as a punishment to her but because she is showing signs of addiction.

Get her to make alist of stuff she's like to do or try. Anything from going to a new cafe for a milkshake to geocaching, earning money from pet sitting or redesigning her room or some new styling for her clothes or hair. get her to set herself some small, achieveable goals in terms of becoming a bit more grown up - cooking a dinner for the family, baking a cake with a friend, swimming a mile, climbing a peak, walking 20k or 30k steps in a day etc.

Help her tick them off. These will give her dopamine hits like gaming does but without the social isolation.

Yoiu could offer to do the same. Go cold turkey with her. No MN, Facebook, Twitter or Insta or whatever you usually look at, for a week, just to lear yur heads and spend time doing stuff together or developing new skills and interests.

You need to cut her off from the devices. For her own good. Introduce say an hour a day or whatever and then that’s it. If she is bored, she’s bored. She will soon find something.

reading, puzzles, drawing, the garden, Lego, jigsaws, baking, card games all popular with my 10 year old son.

Can't you just take away the devices? She will be absolutely foul for a few days but then will adjust.

It sounds like she is addicted. You need to cut it off cold Turkey. That is the best way. Do it a month and reintroduce slowly and see if she can handle it say couple hours Saturday and Sunday.

Give her a limited amount of time on screens each day and don’t let her on them at any other times. She’s 11, you can tell her what is happening, she is old enough to understand the concept of time and if she kicks off about turning screens off then she gets less time the next day.