MC 1.16+
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Player Experience

Experience required to level up now scales less exponentially (vanilla level 30 requires 1392 experience, with this feature active it requires about the same: 1395, BUT, vanilla level 100 requires about 31k experience while with this active only ~15k).
Experience is picked up faster
On death, players will drop 85% of their experience instead of at most 7 levels.

MC 1.16+
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More Experience from Blocks

Ores and Spawners (or more generally Blocks that drop experience) will now drop 3x more experience.

MC 1.18+
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Other Experience

Bottle o' Enchanting now give about 25 experience instead of 7

Anvil repair cap is increased to 1024 (vanilla is 40)
Renaming in an anvil is now no longer costs a level.

Mending is changed to reset the cost to repair an item back to 0, then it's removed.

MC 1.16+
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Nerfed Mobs from Spawners

Mobs spawned from Mob Spawners will now drop half of the experience than a normal mob would.

MC 1.16+
Global Experience Multiplier

Since 1.18.2 experience from all sources is increased by 25%.
Prior to 1.18.2: a config value is available to multiply any experience orb value dropped. By default the multiplier is set to 1.0 so nothing is changed.