Ominous Vaults, when placed by the player instead of generated in a Trial Chamber, are unlocked using Trial Keys and use the loot tables of normal Vaults.
To recreate:
Create a new world with commands and Update 1.21 Experiments enabled
Place a Vault block and use the Debug Stick to set "ominous" to true or use the following command:
/setblock x y z minecraft:vault[ominous=true]
Use a Trial Key to unlock it
Compare the results to the loot tables of ominous/trial vaults
Image 1: Loot from various Vault blocks
Image 2: Loot from various Ominous Vault blocks generated inside a Trial Chamber
Image 3: Loot from several manually created Ominous Vaults
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We're tracking this issue in MC-270062, so this ticket is being resolved and linked as a duplicate.
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