The security account manager (SAM) has determined that SID is already in use in the Forest

function Get-MachineSID {
    [cmdletBinding()]
    param(
        [string] $ComputerName,
        [switch] $DomainSID
    )
    # Retrieve the Win32_ComputerSystem class and determine if machine is a Domain Controller
    $getCimInstanceSplat = @{
        ClassName = 'Win32_ComputerSystem'
    }
    if ($ComputerName) {
        $getCimInstanceSplat['ComputerName'] = $ComputerName
    }
    $ComputerSystem = Get-CimInstance @getCimInstanceSplat
    $IsDomainController = $ComputerSystem.DomainRole -ge 4

    if ($IsDomainController -or $DomainSID) {
        # We grab the Domain SID from the DomainDNS object (root object in the default NC)
        $Domain = $ComputerSystem.Domain
        $SIDBytes = ([ADSI]"LDAP://$Domain").objectSid | ForEach-Object { $_ }
        return ([System.Security.Principal.SecurityIdentifier]::new([Byte[]]$SIDBytes, 0)).Value
    } else {
        # Going for the local SID by finding a local account and removing its Relative ID (RID)
        $getCimInstanceSplat = @{
            Query = "SELECT SID FROM Win32_UserAccount WHERE LocalAccount = 'True'"
        }
        if ($ComputerName) {
            $getCimInstanceSplat['ComputerName'] = $ComputerName
        }
        $LocalAccountSID = Get-CimInstance @getCimInstanceSplat | Select-Object -First 1 -ExpandProperty SID
        $MachineSID = ($p = $LocalAccountSID -split "-")[0..($p.Length - 2)] -join "-"
        return ([System.Security.Principal.SecurityIdentifier]::new($MachineSID)).Value
    }
}

Get-MachineSID -ComputerName AD1

(Get-LocalUser |Select-Object -First 1 -ExpandProperty SID).AccountDomainSid.Value