Ensure no naps during the day or afternoon. If that’s not working, see your doctor for Melatonin. It’s natural- we all release it in our brains. Some kids have a little more difficulty producing it and need that additional help. Other factors is he being mentally stimulated throughout the day and physically active? Is his tummy fall? GOOD luck

Have you tried a set bedtime routine eg: bath, story, quiet music? Quiet music worked a treat for my kids. Also no technology for an hour before bed time.

Is he calm before falling asleep? May need a little help. Some soothing music or story? Otherwise have a chat to Gp just to rule out anything else if you are worried

Generally, a wind down routine that’s implemented on a daily basis has great results. Eat tea, maybe some tv watching, then a bath and brush the teeth. Followed by a story read to him in bed. If he has other issues, a GP visit might be needed. A friend of mine got a prescription for melatonin for her 4 yo that wasn’t sleeping. But he was worse then your 6 yo, often sitting up til after midnight!

You say you struggling your 6yr old for bed. What type of behaviour does he show ? And what do you do before bed ?
Personally I believe in a consistent routine and structure before bed. When he struggles to settle you could start earlier with that. For example bath after dinner, dimmed lights, activities to slow down like reading a book together and no screen time.
Also it may be good to look at diet as refined sugars make many kids hyper.