I believe sleep issues are one of the biggest problems in the world, literally. You seem to have explored most of the options I know about so I don't have much to offer.
Is your room totally blacked out?
Type of Magnesium makes a difference for this purpose - Threonate is best bis-glycinate is next and way cheaper.
Have you seen Hubermans protocol? Too much for me to describe here but check it out, podcasts, his sites etc. he has a page that sums some things up but I can't remember where it is.
I think he is against melatonin too and can present a good arguement for why.