Hello, good day and thanks for your question. Sorry to know on what happened that you have missed the migration for your Minecraft account.
For this, the mandatory migration window for older Mojang accounts to transfer to Microsoft accounts officially closed on December 18, 2023 and there were extension that happened along the way to give ample time for the players.
Because this hard deadline has passed, unmigrated accounts are permanently deleted, and Minecraft Support no longer possesses the tools to recover or migrate them.
Please see the link below as a reference with regards to this as well.