Recommendations Looking for mc from earth with immortality as his cheat

how close to immortality are we speaking?

indigosharpe's Pitch black dreams takes it in an interesting direction (cthulhu / primordial being),
there's also the Webnovel original prime being (zero or something), god's would be re;write by whocares, and transmitigation retiree on RRL is quite immortal. The novel's redemption, Never Die twice (RRL), Perfect Run (RRL) and Bleakwalker, and I'll throw in relevenace and the world flying off the tracks.

Apocalypse Cockroach, Power and wealth (a literal cockroach / invicible figure), Pursuing Immortality, The Monk That Wanted To Renounce Asceticism (becomes a god like figure), a valiant life, Omniscient Reader (kinda...eh not really).

some oddballs
spare me, great lord, cthulhu gonaflon, 24 hours after, psychic gambler stuff

There's various god like figures, OP figures, can't die / revert time.

If you're looking for the wuxia / xianxia stuff, I recommend the classic alchemist dan god reincarnation / JP returner's magic those guys are quite unkillable. Korean's genre is more of the vulnerable, lone wolf, but mostly mortal type stuff with some of the darker JP novels edging in that direction. Re;zero would be a good example of time travel, erased (boku dan inai machi)....

then we degenerate into ISSTH, BTTH from Wuxiaworld I think / gravitytales (-> webnovel???)