As others have noted below, it's not just international. I had a package shipped from Seattle for my business the week before Thanksgiving (US) and they shipped USPS against my wishes. It has been "in transit" since Nov 28. It was an urgent shipment, which compounded my anger. My wife sent out 40 Christmas cards on Dec 15th, most domestic, and only a fraction of them have been received.
It's a combination of Covid affecting the workforce (less labor available) and the budget cuts enacted over the past year to cripple the USPS They were pretty effective in their objective.