Okay, so the first thing that comes to mind is definitely the 'I Got a Cheat Skill in Another World and Became Unrivaled in the Real World, Too' series. That one's right there in the title. The MC finds a door to another world and uses the skills and items he farms there to become OP back on Earth. It’s a huge part of the plot. I see a lot of other isekai that use it as a mechanic, but it’s often just a launchpad for the story. Stuff like 'In Another World With My Smartphone' or 'The New Gate' has elements of it, but the farming itself isn’t always the main draw—it’s more about what the cheat ability unlocks.
Personally, I find stories where the cheat is specifically a game-like skill to cultivate land or spawn resources more satisfying for that 'farming' itch. There’s a webnovel I can’t remember the exact title of, something about a guy who becomes a farmer in another world and his cheat is just insanely efficient agriculture. The focus is on building up a territory from nothing, which feels like the purest form of the trope. It's less about flashy battles and more about the systemic exploitation of a world's rules to create abundance, which can be weirdly calming to read.