Organisms are evolved to utilise short life-spans to quickly adapt changing environmental conditions.
Let’s assume humanity finds a cure to death and also without dwelling into dystopia that this finding is cheaply available to everyone. What will most likely happen is that bad ideas will haunt the humanity forever as older generations won’t die and remove their bad ideas with them. There might come a point that humanity will completely collapse due to rule by elders where they can be expected to accumulate much of the available wealth. So bad ideas of older generations can lead to total collapse of species.
Honestly I don’t see anything other than dystopia occurring with the cure to death, regardless if it is expensive or cheap.
I’m also impressed people want to live forever, this is something I cannot possibly understand, don’t people at least want to see what is at the other side? Do they think they will never get bored from material existence?