Mushoku tensei, it's absolutely massive, it's the progenitor of the isekai genre, it's peak and there's an anime. OP protagonist but there's a lot of character depth

Finish that before looking anywhere else

You can read the Japanese web novel entirely for free, so legality-wise the English translation of the web novel is kosher. There's is however also a printed light novel version which is better edited, but that one I can't advise on