As others have mentioned, you can invest in the stock market within your 401k, though your options can sometimes be limited or saddled with high fees depending on what broker the 401k is through.
If yours is through a shitty broker then you might be better served by opening an individual retirement account (IRA), likely a Roth IRA given the limited info you’ve shared. You can open one with a broker of your choice, so go with one of the better ones like vanguard or fidelity. Using tax advantaged retirement accounts will always beat saving your retirement money in a non-tax advantaged one, all else being equal.
Don’t carry water for people who would let you die to increase their mountain of gold a little. What you’ve described might be true of millionaires, even multi millionaires; but no one gets to a billion dollars without stepping on those below them in the pursuit of more money than one person could ever spend in their lifetime.
Being a billionaire is pathological, if the human race was a biological organism and one part of it started hoarding that many resources, we would call it cancer and cut it out.