The Mig-21PFM even says in Wikipedia that it was possible to install a K-5MS PARL missile on it
He had a new ejection seat, unlike what we have in the game as just throwing the pilot out of the fuselage with his hands
In addition, if you go to Google Pictures and write Mig-21PFM, there will be a photo of how it takes off with Rocket boosters, that is, it had suspension points for installing external rocket boosters
Application:
Rocket busters on the takeoff:
Attention: everything is taken from open sources (no secret documents)
https://com.wikipedia.org/wiki/ΠΠΈΠ-21