Depends what you mean by farm, but if you mean mob based farms, I recommend none, because they're prone to getting broken or nerfed in consecutive updates.
I can only recommend a crop field of sorts to keep you fed for survival purposes, and perhaps trade a surplus with Villagers for emeralds, but even then Villager trades get nerfed once in a while too so they're not reliable, they already added a cool down to trades which doesn't really make the game anymore challenging, just more time consuming, raids offer more of a challenge than a simple minded nerf to trades, although they're not without their flaws, even though you can make a raid farm, this is risky because the combination of Evokers, Witches, Ravagers and Vexes are hard to deal with, worst of all they can kill off your Villagers.
I'd love to build a complex farm with redstone again, but right now I don't have the motivation to, because I know it's only a matter of time before Mojang ruins it forcing me to rework the contraption later on or give up altogether, and that's hassle I'd rather not waste my time with. I play Minecraft to relax and socialize with friends and share ideas for builds and collect resources by mining, same with lots of other people, but over time the game steadily became more boring and grindy, so like other people I move onto other things, I have at least a couple of friends who went off Minecraft because of the asinine rules that get imposed on us, I also have a friend on Steam who says Minecraft is boring, and it is.
I will be honest and say I do miss the days when you purchased a game and it was an actual final build, meaning it couldn't be tampered with any longer by the developers once it hit the store shelves, this meant that you could experiment as much as you wanted with your game and you always knew it worked, but those days are long gone.
The farms that i recommended thankfully dont require much redstone,and can be removed and replaced easily if needed.Mojang mostly screws up redstone-heavy farms (if that makes sense) and stuff involving villagers (cause they love to disappear).