Originally Posted by
Seat 2A
I'm not sure which year you reference here, but I'm fairly certain Syrianair was flying an SP on a Teheran - Damascus - Caracas route in the early 2000s. That may well have been the last SP in scheduled service. Also, Iran Air would be an excellent candidate for operating the last SP flight, possibly within the last 10-15 years.
Looking at
https://www.747sp.com/ (an extremely granular resource!) Syrianair was operating its two SPs up until sometime in 2008. They flew them to RUH for maintenance in 2011 but the US government revoked necessary licenses for Boeing to carry out repairs, and the aircraft have been stuck there ever since. Iran Air's EP-IAC left commercial service in 2016 after failing a safety inspection, and had its last reported ferry flight in 2018.