There’s a difference between business plan and Business Plan, so to speak - a formalized document with a pretty standardized format you used to have if you, for example, wanted to get a loan from a bank.
It’s mostly gone away, but there used to be endless arguments about whether a startup should have a formalized written business plan https://en.m.wikipedia.org/wiki/Business_plan. Business schools taught all the MBAs to write them, and everyone used to argue about whether a startup ought to have them.
Today I’m not aware of any VC or investor that requires/wants a Business Plan, almost everyone has settled on a standard pitch deck if anything (though one-page ‘memos’ are becoming a thing, and some investors even eschew those). A few business schools somehow still tell you to create a business plan if you want to raise VC. I invest in ~100 startups/yr and will see a handful of Business Plans sent to me, but not many. I don’t read any.
YC Continuity today would likely look at a deck and definitely ask questions, but still wouldn’t require a Business Plan.
PG probably wouldn’t ever even look at a deck.