I have exactly the same trouble as you. My son is now 12 and after 5 years of tearing our hair out over it, we’ve stopped waiting for him to fall asleep. We now just make sure he stays in his room and take all the devices away. He isn’t asleep when we go to bed at 10.30pm but by then he’s resigned to his fate and does eventually fall asleep.
We changed our evening routine so he comes off all devices at 7pm, and we have about 90 minutes together we we play games, talk and read together. It’s exhausting (because by then we just want to totally switch off ourselves) but we think giving him this attention at that time helps him get a lot of wriggles out. He then is fairly quiet, not sleeping usually, but just quietly laying in bed talking to his teddies or going through some cards or something. He also has an Alexa in his room that he talks to and plays quiet games with. Sometimes he does guided meditations- some of the ones on YouTube for kids are excellent (audio only).
I have to keep reminding myself that if we can’t get him physically asleep, we have to accept the next best thing which is low stimulation rest time with no screens.
It is very frustrating I totally agree and we’ll never give up trying to encourage better sleep habits (gift of a lifetime) but we now have made peace with a “next-best” evening routine.
I also have a 15 year old who used to sleep brilliantly and now he’s a slave to his phone. The battles never stop!