Earlier quoted context omitted.
Why would you need to create a local account? You can just not choose to store the keys in your Microsoft account during BitLocker setup: https://www.diskpart.com/screenshot/en/others/windows-11/win... Admittedly, the risks of choosing this option are not clearly laid out, but the way you are framing it also isn't accurate
All "Global Reader" accounts have "microsoft.directory/bitlockerKeys/key/read" permission. Whether you opt in, or not, if you connect your account to Microsoft, then they do have the ability fetch the bitlocker key, if the account is not local only. [0] Global Reader is builtin to everything +365. [0] https://github.com/MicrosoftDocs/entra-docs/commit/2364d8da9...
The question is do they ever fetch and transmit it if you opt out?
The expected answer would be no. Has anyone shown otherwise? Because hypotheticals that they could are not useful.