“LOL? Superman doesn’t kill?! Superman HAS always killed, but always tried not to. Only in extreme circumstances.”
As I already mentioned - in the Golden Age, on rare occasions, he was indifferent to the fate of an evil doer - but that’s not killing.
He killed Mr. Mxyzptlk at the end of the Silver Age, but he gold krypto’ed his powers away (he was no longer Superman) as penance (and it was non-canon - there have been non-canon stories of “Superman” in nearly every situation imaginable - it is not part of the Superman legend).
The only true example of Superman killing was John Byrne’s Superman (and this 1988 story is what MOS was based on), but that story kind of dissolved in canon and even then he banished himself into space as penance.
In the Superman vs. Aliens cross-over, after Superman realizes what he’s dealing with, he kills the Alien creatures, considering them “vermin” (they wiped out the remaining Kryptonian race except for Kara).
So there you have it. One non-canonical example and one barely canonical example. That’s two examples in his 75 year history and thousands upon thousands of stories.
Superman has *not* always killed. My Superman doesn’t kill.
I had always assumed that Superman killed Zod and the others at the end of "Superman 2" . If not, what happened to them?