Your Minecraft name is usually your Gamertag for whatever platform you play on. It identifies you to other players in multiple games, including Minecraft. There are ways to change your Minecraft name ...

Select “Profile Name” Change to the desired name and save This name change doesn’t effect the Gamertag found on the Xbox account, and will only be shown when playing Java edition.

How do I find my Minecraft username? On the change name screen, you can see your previous name located right after the field “Current Java/Bedrock Profile Name”.