In addition to the usual, standard, Windows has hidden virtual accounts. On their behalf, various services are launched and run in the system. With PowerShell , you can get a list of all accounts.
Standard accounts
get-wmiobject -class "win32_account" -namespace "root\cimv2" | sort caption | format-table caption, __CLASS, FullName
Virtual Accounts
get-service | foreach {Write-Host NT Service\$($_.Name)}
The virtual account can be found and added in the security properties of the file or folder. For example, the TrustedInstaller account: click the "Modify" - "Add" buttons, enter NT SERVICE\TrustedInstaller in the field and click "Check Names".
The system will find the required account and after confirmation it will appear in the list.