So when Eugene IV taught that Jews and Muslims were automatically damned, he taught correctly, and it was not open to change. Except that Lumen Gentium did change it, even though traditionalists pretend the teaching did not change.

That's a major problem I have with traditionalists: They claim that teachings do not change, a claim that can be supported only by either dishonestly twisting the teaching to make them appear to match (a line from Gilbert and Sullivan's Trial By Jury entered my mind, "a very nice girl you'll find her
She may very well pass for forty-three
In the dusk, with a light behind her") or by outright lying about it.