Does your employer offer you a match on your 401k contributions? That’s free money regardless of how the 401k is invested so you definitely want to keep that going.

Even without that generally speaking you’ll still want to continue contributing to your 401k. Remember that a 401k is long term retirement savings, the market will continue to rise/fall during your employment over the next x years. You’re not required to invest 100% in U.S. specific index funds, in fact most people would recommend allocating a mix of U.S. / International / Bonds e.g. the “lazy” portfolio is one of the more famous recommendations www.bogleheads.org/wiki/Asset_allocation

Or for just set-and-forget you can invest in target date retirement index funds if your 401k offers them (most 401k plans offer those nowadays).