How to handle anxiety (?) about bed time

My 4.5 year old has struggled with bedtime all his life. He stalls like crazy every single night even with a consistent and predictable bed time routine. He takes an hour or more to fall asleep even though he doesn’t nap and seems very tired. He also makes it extremely difficult for us to leave his room if he’s still awake. We’ve tried so many things: night light, heated stuffed animal, sand timer for cuddles, 5 minute check ins, no screen time for two hours before bed. With our constant effort he has not improved after all this time. He’s starting kindergarten in the fall and has to wake up early 5 days a week so he is going to be so tired if he doesn’t start falling asleep sooner. He’s generally a pretty well behaved kid who can be reasoned with but bed time has always been a different story so I’m wondering if it’s anxiety? But I don’t know why or what to do about it. Does anyone have any experience with this and can offer some advice?