Scrum Meeting should be finished in 15 mins - max 20 mins. IF PO joins scrum call it damages teams autonomy and most of the time PO might jump in and say hey dont do this or that like this and then things can turn into long debatable discussions.
PO Should not be involved in scrum call , let developers do the best based on user stories description if at all there are any blockers, scrum master has to facilitate it and can pull PO in scrum call meeting if required.