Most (all?) 401k plans limit you to a pre-picked list of ETFs and mutual funds you can invest in. Not to mention the standard advice for decades has been 'broad market index fund'.
Afaik this is the first time that an IPO is big that it immediately gets a significant share of a broad market index fund. The rules among the providers are actually quite diverse, so it's complicated. The Rational Reminder podcast discussed it in April: https://rationalreminder.ca/podcast/406
Their conclusion: It might be bad, but so be it. No need to change strategy.
Good thing is that index funds don't hold stocks at market capitalization but only at free float value. So a company whose shares are mostly held by founders, employees, and strategic investors gets a weight well below its headline valuation.
I believe it's the opposite :)
All major indices (S&P500, MSCI, FTSE...) use free-float adjustments. And recently also NASDAQ - they've changed to cap of 3x the value of free-floating shares.
If your plan uses Fidelity you can move your 401k into Brokeragelink and that lets you pick individual stocks. Schwab, TIAA, Alight and some others also have something similar.