Lore fans what is dark star thresh and is he canon ?

Dark Star Thresh is basically Galactus. And no he is not canon

Cosmic destroyer of worlds

Safe to say until you hear or see otherwise from Riot, skins are not cannon (at the very least, not cannon in the current timeline. For instance, Elementalist Lux and SG Udyr are basically them once they master their powers/stop being drunk)

Skins aren't main canon. Some represent events that occurred in the mainline canon (Dragonslayer Jarvan), or outfits from periods of a champion's life (Pre-Void Kassadin), but they are the exception rather than the rule. DST is not one of them.

Dark Star Thresh is basically the embodied form of entropy. His purpose is to destroy everthing and sniff out every light.

No, he isn't canon, expect a handful of skin, all skins are usual alternative fantasy and play in a different universe.

Dark star thresh isnt canon but there might be something similar lurking as n space. Due Aurelion sols quote about the terrors in space and how the people of runeterra should pray it never come for them.

Thresh is a cosmic entity who serves and feeds the Dark Star in the hope that it will eventually devour the universe and himself.