@Atharva Deshpande, Thanks for posting in Q&A. For your enrolled device, please check if it is Microsoft Entra joined. if yes, this join type can allow all the organization Microsoft Entra users to login. This is by default.
For the user you mentioned, is this a local user. If yes, we can remove the local user via PowerShell Script
Remove-LocalUser -Name <user name>
If the users on all the devices are the same, we can consider deploy the script via Intune.
https://learn.microsoft.com/en-us/mem/intune/apps/intune-management-extension
Hope the above information can help.
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