I think the point is a bit more nuanced and has to do with the authors conception of the self. He argues that even if you got immortality and lived a great life at some point You would stop being You so you might as well have died anyways. I think it’s a bit silly. But if you believe that enough alteration of the self results in its death, a sort of Self of Theseus, then I think it’s a consistent opinion.

> His argument is precise: the desires that give you reason to keep living (he calls them categorical desires) would either eventually exhaust themselves, leaving you in a state of "boredom, indifference and coldness", or they'd evolve so completely that you'd become a different person anyway. Either way, the You that wanted immortality doesn't get it. You just die from a lack of Self rather than through physical mortality.