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.
Edit to echo the flowchart from one of the other comments: imgur.com/u0ocDRI
This is the core of sound personal finance strategy in purified form. Great resource!