Here are the best ways to do that after the 1.18 update ... but they make XP an afterthought for players because they'll have so much. A kelp XP farm, in which dried kelp is used to smelt kelp ...

Instead of grinding for XP ... wool farm is also helpful. Setting one up with a sheep, a dispenser, and shears is somewhat difficult, but it makes collecting wool so much easier. Kelp farms ...

but in 1.18, the best way to automate experience farming is by growing lots of kelp. Players can create a Kelp XP farm ...