While I also practice Bogle's approach from The Little Book of Common Sense Investing, even with this baseline there are some subtleties.
-VFIAX is currently $707/share. Fidelity's FXAIX does not have to be purchased in increments of a share price, and this fund's expenses are lower.
-There are versions of the S&P 500 for taxable accounts that minimize capital gains.
-Vanguard has a total-market index, VTSAX, that is mentioned in the book.
-Vanguard also has a non-U.S. total market fund, VTIAX, that avoid the current CAPE problems of the U.S. market.
Claude is very familiar with Bogle's approach, likely because the pirated book was part of the training set.
Though you don’t directly say it, your comment strongly implies that you can’t buy fractional shares of $VFIAX. (You can, same as $FXAIX, $VTSAX, etc.)