When using /enchant on Netherite items, the items won't update until you attempt throwing them onto the ground, if you try to move it in your inventory, it will be locked to that slot until you try throwing it onto the ground, it will appear back into your inventory with the enchant used.
Thank you for your report!
We're actually already tracking this issue at MCPE-65389, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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