I developed that issue once I got older. It fucking sucks. All the old "keeping a regimen" tricks to avoid "falling asleep insomnia" don't work.
Try not to nap, but don't nap at all in the evening. That's poison, you've basically started your night's sleep.
Keep trying to go back to sleep even if you don't really want to. Part and parcel of this is to not look at a clock when you wake up. Only finally get up when you realize you are laying there for a while pretty wide awake.
Your MMV on this one, but... try to get in touch with your dreams more through dreamwork, DMT, Blue Lotus, or all three (not together). That can have a surprisingly big effect.