I think it might be restating the obvious to say that a company pulling in 100M+ is no longer a startup, it's an established (even if relatively new) company in aggressive growth mode.
I joined my last company about a year before they raised a Series C that brought total funding to $95M, and I think that by almost any other definition it was a startup before and afterwards.
(And it was enough of a startup to do a "hard pivot" to something largely unrelated when the pandemic destroyed its core business model, instead of shutting down.)
Yes $100M is a lot in absolute terms, but depending on what you're trying to achieve, how many people you need to achieve it, and what your timeline is, $100M might not be so crazy in context.