my Terminal Insomnia just doesn't go away

I'm having Terminal Insomnia for more than 2 years now. I would fall asleep relatively fast but then would usually wake up after 3-3.5 hours (usually at 4-5 a.m) and afterwards I wouldn't be able to fall asleep most of the nights. I have tried sleep restriction for about 2 months but it didn't improve the situation. I also made a test in a sleep lab, but they did not discover any disorders. Any ideas what might help at this point ?

Hm, have you listened to any of Huberman Lab's podcast episodes on sleep?

Also personally, I've found some simple things helpful like: white noise machines, 2 layers of blackout curtains, keeping the room cold, no visible alarm clocks, just taking a sip of water before bed (enough to be hydrated without having to take a leak), and not looking at screens for an hour or two before bed and then NOT AT ALL until my alarm goes off in the morning (In my experience, if you wake up and check your phone even just for the time, you're screwed).