Does your daughter understand why she's struggling to concentrate, or is it just "I want to, so whatever" for her?
I agree that bans don't work, but there's another thing: often a teenager doesn't see the connection between their behavior and the result. Try suggesting that she track herself how her attention and grades change depending on screen time - you're not the one counting, she keeps a simple diary for a week or two. People change their behavior way better when they find the patterns themselves than when someone points out the problem to them.
After that, you can already discuss it not as "you have to," but as "how can we make it so you can study and not feel like you're being punished." Maybe it'll be a call to a friend before homework, or 15 minutes of TikTok as a reward after finishing an assignment - something specifically for her, not your version. The main thing is that she'll be a co-author of the plan, not a victim of a ban.