Since 1.21.51 was released, I was not able to unlock any achievement.
I am an experimented player and I performed several tests to make sure this bug occurs in this version in Windows 11.
I repaired these apps: Microsoft Store, Xbox app, Xbox Live, Xbox Game bar.
I uninstalled and re installed above apps (clean installation).
I created several vanilla worlds (survival, no texture packs, no BP, no RP, no cheats, no commands, no datapack.... In other words: FULL VANILLA).
I told a friend to host a world where he can unlock achievements on Xbox console.
There are no datapacks in my client.
There are no resource packs in my client.
There are no behaviour packs in my client.
My client is full vanilla.
I have never enabled creative/adventure mode.
I have never enabled Beta API, experiments, etc. I always play vanilla worlds.
I am not offline in xbox social.
Xbox app and services are running on background correctly.
Xbox game bar seems to work properly.
I have tried to unlock several achievements (i you mind im talking abount just one achievement i cannot unlock you are wrong).
There are some achievements I have tried to unlock: Craft a dispenser, Gatos a mansalva (i dont know how to say it in english), cook using kelp block, get all wool colors.
Have you tried the solution in this comment?