Ominous Spawners placed by the player in creative 'converted from trial spawners with the ominous bottle' don't affect the loot drops and difficulty properly.

When placed by a player in creative as a trial spawner and converted into an Ominous spawner using the ominous bottle to gain trial omen, the Ominous Spawner fails to enhance the gear of the mobs and drop items from the correct loot table. However, the spawned projectiles around the Ominous spawners still appear, as well as the visual effects.

On PlayStation 5, so no pics or video, but I’m sure you could recreate this in-game, as it is a consistent occurrence.