What is the highest xp farm that I can create on a singleplayer vanilla Minecraft 1.14 world? I'm not concerned on how long it would take to build, I just want to make something that has a ridiculous xp rate for singleplayer[/p]
I would love to create something like this where I can use nether portals to funnel mobs to one spot: (can I even use portals to increase rates in singleplayer 1.14?) [/p]
You cannot use portals to increase spawn rates in any version of Minecraft, but you can use them to fling mobs off the mob cap so that more can spawn (mobs in other dimensions don't count towards the cap) within the limited space available.
The spawn rate is fixed at 2-4 mobs (4 being the maximum size for a pack spawn, 2 being the minimum size for a pack spawn) per chunk per gametick for most mobs, so the name of the game is how fast you can kill them or push them through a portal.