It’s happening that when I try to equip elytra I just don’t equip when I’m wearing a netherite breastplate

You can't have a chestplate and an elytra on at the same time.

Thank you for your report!
However, this issue is Working as Intended.

The report you have submitted is working as intended: You cannot have both Chestplate and Elytra equipped at the same time.

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Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.

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