Looking for stories where the MC has close to no talent in the field he's in, no cheat code or some grandpa in a ring or something either; he mainly relies on pure sweat, blood and tears to progress. A regression story's fine as long as his "regression" doesn't assist him too much unlike most regression stories. A good example of this would be "Possessing Nothing" where the MC gets a second chance, but the fact he didn't get far in his first life makes his regression not all that effective, not to mention his abyssmal talent.
Everyone else is Returnee (?) - MC works hard for 1000 years in a time stopped earth. Goes from talentless (ignoring the stealth) to all rounder through effort. Clearing an Isekai with the Zero-Believers Goddess – The Weakest Mage among the Classmates : weak MC but always busy practicing. His only cheat is a really sharp knife.
Undefeated God of War, Avalon of Five Elements(Discontinued) - are two works from Fang Xiang where MC's are at the lower end of talent spectrum, at least compared with World of Cultivation MC's ungodly talent.
Well record of mortal's journey to immortality is the closest you can get. He is the most talentless mc i have seen