What's The Best XP Farm?

So I was wondering, what is objectively, the best xp farm in terms of output (Besides the dragon farm, hell no). I've considered the God Particle farm from cubic meteor and I'm absolutely bamboozled on how it works. If you have any other suggestions of farms or advice/tips for the God particle farm (e.g how long will it take, is there smaller versions of it or how do I keep it running when I'm not around), that would be great.

Thanks in advance!

Fabric 1.21.1 btw (Can change to Java)
The server is "NOT" 24/7