Summary

In vanilla, mobs only drop experience and/or rare loot when killed by a player, not when killed by their environment. With this mod, mobs will always drop experience orbs and loot, regardless of cause of death. This is useful for people who like to build passive mob farms and such.

Installation

Requires Fabric Loader and Fabric API.
Configuration

Since MC 1.17.1, the mod config screen has been replaced with gamerules in order to allow configuration per world.

If you have cheats disabled in your world, you can temporarily get cheat permissions to edit gamerules by opening your world to LAN.
Always drop XP

Control whether all mobs drop XP when killed, regardless of whether a player killed them.

/gamerule always-drop-loot:alwaysDropXp true: mobs will always drop XP regardless of how they died. (default)
/gamerule always-drop-loot:alwaysDropXp false: vanilla behavior; mobs will drop XP iff killed by a player.

Passive XP modifier

Control the amount of XP dropped when mobs are not killed by a player. Only applies when always-drop-loot:alwaysDropXp is true. The value set in this gamerule is multiplied by the mob's natural XP drop value, and the result is rounded to the nearest integer.

gamerule always-drop-loot:passiveXpModifier 1.0: mobs will drop the same amount of XP regardless of how they died (default)
gamerule always-drop-loot:passiveXpModifier 0.5: mobs will drop half the normal XP when not killed by a player.

Loot drop mode

Control whether the killed_by_player loot condition always passes, regardless of whether the entity was killed by a player.

/gamerule always-drop-loot:lootDropMode ALWAYS_AS_PLAYER: the killed_by_player loot condition always passes (default)
/gamerule always-drop-loot:lootDropMode NEVER_AS_PLAYER: the killed_by_player loot condition always fails
/gamerule always-drop-loot:lootDropMode VANILLA: vanilla behavior; the killed_by_player loot condition passes iff the mob was killed by a player.
/gamerule always-drop-loot:lootDropMode VANILLA_INVERSE: the killed_by_player loot condition passes iff the mob was NOT killed by a player.

Credits

big thanks to sargunv for creating the mod, the description and making it open source.
https://modrinth.com/mod/always-drop-loot
The only work I did was port this to the latest version.