My son also has ADHD and is aged 8. He is not on any medication so I can’t comment about that but we have a range of techniques we use at bedtime. Have you tried any of these or a combination?
1) screen off 1 hour before bedtime
2) bedtime is the same time every day
3) a routine of get washed, clean teeth etc PJ’s on
4) a chat about anything he or she wants to talk about (really listen and comment but limit to 10 10-15 mins)
5) followed by a story read by a nightlight or torch (to encourage relaxation and sleep)
6) followed by a cuddle for another 10 mins
7) then I say goodnight and leave him to get to sleep himself.
Just some suggestions as one mum to another