Melatonin. Magnesium. No screens after nine. Cooler room, white noise, earlier bedtime. Most people work through that entire list before they realise something: those fixes are all aimed at falling asleep.
But if you're reading this, falling asleep was never really your problem. Staying asleep is. Those are two different systems in the body, and the second one is rarely what gets addressed.
A sleep researcher recorded a short presentation explaining what's actually happening in the body during that window, and the simple nightly routine his patients now use instead.