https://deoxy.org/index.htmlThere's that if you mean schizo delusions with grains of truth.
If you mean fully realized magical/alchemical/whatever systems with rules and lore or whatever
https://archive.4plebs.org/tg/search/subject/worldbuilding/most of it is fucking shit but autists can't be choosers. Also you could check out All Tomorrows or the Silmarillion but you probably know what those are.