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 ...