The base game keeps things simple with iridium quality coming from reaching farming level 10 and using deluxe fertilizer, but if you're interested in more depth there's some great mods that add prestige mechanics. Skill prestige and walk of life are the main ones you'll want to look into, letting you reset maxed-out skills for some really nice permanent bonuses. The nice thing about these mods is how they let you stack different perks together, so you can combine stuff like the artisan bonus for better wine prices with faster crop growth from agriculturalist, which isn't possible normally.

A good approach is starting with the artisan profession, since that +40% bonus to processed goods is huge, and then working your way through the other skills you want to prestige. Each reset costs between 1-2 points depending on the profession tier you're going for, and you'll unlock some interesting stuff like faster machine processing or combat limit breaks if you're into that side of things.

Something worth knowing - while the modded prestige systems add a ton of depth, getting basic iridium quality items just needs max farming and good fertilizer in the regular game. The mods basically take that foundation and let you build on it with reset bonuses and expanded progression past level 10.