Generates an object identifier (OID) using a GUID and the OID prefix 1.2.840.113556.1.8000.2554 (or any other you like). Inspired by this: https://gallery.technet.microsoft.com/scriptcenter/Generate-an-Object-4c9be66a

New-ADCustomAttributeOID.ps1

# Inspired by this: https://gallery.technet.microsoft.com/scriptcenter/Generate-an-Object-4c9be66a
# Generates an object identifier (OID) using a GUID and the OID prefix 1.2.840.113556.1.8000.2554 (or any other).
function New-ADCustomAttributeOID {
    [CmdletBinding()]
    [OutputType([string])]
    param (
        # OID Prefix
        [Parameter()]
        [string]
        $Prefix     = '1.2.840.113556.1.8000.2554'
    )
    [string]$GUID   = [System.Guid]::NewGuid().Guid.ToString('N') # See: https://learn.microsoft.com/en-us/dotnet/api/system.guid.tostring

    [int]$step          = 4

    [string[]]$Parts    = ,$Prefix + @(
        for ($i = 0; $i -le 26; $i += $step) {
            if ($i -ge 20) {
                [int]$step  = 6
            }
            [uint64]::Parse($GUID.Substring($i,$step),[System.Globalization.NumberStyles]::AllowHexSpecifier) # See: https://learn.microsoft.com/ru-ru/dotnet/api/system.globalization.numberstyles
        }
    )

    [string]$OID    = [string]::Join('.', $Parts)

    return $OID
}

About OID prefix:Microsoft Learn

BTW, I suspect that everybody use the sample root OID "1.2.840.113556.1.8000.2554" from the article.

Yes, it's base OID for customer usage, but I think it would be better to append some child bytes before creating custom attributes and classes in the your AD schema.