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?
If they are just reinventing stuff they already know about, then possibly.
If the have to start from scratch and with no prior knowledge then definitely not. Two significant drivers of invention are necessity and interactions with/observations of environmental factors and those will likely be missing.
Eg the role of cowpox in the smallpox vaccine.
there may be other ways to reinvent the same things though
True. But will there be reason to?
boredom