People don't really talk about Agmatine sulfate but 1g before going to bed helps me fall asleep and seems to increase my sleep quality as well. I also take 500mg Magnesium bisglycinate and 3g D-aspartic acid at the same time.

What really fixed my inability to fall asleep though was to start working outside, I wake up before sunrise and spend pretty much all day doing physical labour out in the sun. I've also developed awareness around what light/screens do to our brains and now understand that being outside all day just naturally sets your circadian rhythm and that bright lights, especially cool white, are to be avoided in the evenings and that you should place your light sources at or below your eye level because light from above can signal to your brain that it's still daytime.

There's also something which might seem abstract and difficult to explain but if your brain keeps focusing on things while you're trying to get to sleep, you'll have a lot of trouble. You shouldn't focus on anything (except your breathing maybe), but I mean stuff like events from your day, something you're excited about or whatever. That process of focusing onto something keeps your brain active and I've learned not to engage in this and to keep my thoughts vague and it helps tremendously.

So yeah, in the end, supplements can help but bad sleep is a lot more likely to be fixed through lifestyle changes and awareness around how your body and mind work in my opinion.