How would an immortal society evolve though? Both biologically and socially. If they are anything like humans, you need the old generation to die for new knowledge to take hold.
Humans haven’t significantly evolved over the time it took for civilization to emerge. Humans evolve socially as they get older. Who can say what the psyche of such an alien species would be? Maybe we can add “willing to consider new ideas” to the list of assumptions that would have to be true for this scenario to play out.