Let’s say we left one single very smart guy (not necessarily with the knowledge: they may be able to understand hard stuff when taught it, but not know it already) alone on a copy of the earth. That person is also immortal. Could that person, by themselves, gain back all knowledge, maybe also experimental, or even surpass that is already available to us right now, before the planet gets inevitably engulfed by a sun turning red giant?
there may be other ways to reinvent the same things though
True. But will there be reason to?
boredom
Hopefully boredom will lead to better inventions than flurocarbons and atom bombs.
Or investors and earning calls.