Yup….
MiG-21 BISON in the IAF!. Heck it even took out some F-15 during Cope India 04 IIRC ๐ฎ ๐ฎ ๐ฎ (I have also heard of a even nastier boy called MiG-21-97, but not sure what happen to that)
Some others:
MiG-21 Lancer
MiG-21 2000 (EL/M-2032, DASH etc.).
The best if you look at radar and weapons systems but these upgrades remain old fighters due to flight capabilities, airframe and engines. If one shoots down an F-15 (from BVR) its just a matter of luck. If they are at close range they are sitting ducks. In modern warfare AWACS and flying command posts are used so these “upgrades” will not stand any chance.