Hi Imran,
I am Dave, I will help you with this.
Windows creates hidden security accounts in the background of the operating system, they all begin with S-1-15-XXXX, all Windows systems have those accounts, they are used for administrative tasks like Windows Security, installing updates, file management...etc. those accounts are normal and rest assured you have nothing to worry about, you should never try to remove those hidden accounts.
You cannot be serious? Are you joking!?!
So you are tellimg me, Microsoft has created "back doors" into my OS for the purposes of modifying the OS without my knowledge? ( actually I already know that, but it does not make it secure, or correct practice.)
Have you ever heard about Operating system security, OS security hardening methods, and secure account management baseline and best practices ?
Have you ever applied security using Indetification and Authorization Control and Access Controls?
If the system says a user account is "unknown", it is a security vulnerability waiting for exploitation by a hacker.
Any account created externally without the owners knowledge is called AN EXPLOIT!
Read and apply the Microsoft OS Security baseline best practices PLEASE!!
https://learn.microsoft.com/en-us/windows/security/operating-system-security/device-management/windows-security-configuration-framework/windows-security-baselines
Would you mind supplying me your bank account access information, I'm unknown to you and it is normal for you to give access your financial secure data to unknown entities. Sure, "nothing to worry about" ...
User Accounts should be named specifically for their purpose - Admin permissions are created for that explicit purpose, and ADMIN's Jobs is user account management,
You might want to READ and PRACTICE this NIST Guide to General Server Security: https://nvlpubs.nist.gov/nistpubs/legacy/sp/nistspecialpublication800-123.pdf