Crypto is extremely unstable, High risk High Reward. Also a lot of scams and rugpulls.
Stock exchange is still risky, but slightly less so, though you have the caveat of it being backed by currency/government. For better or for worse.
Land is a similar situation to stocks, but even if the land-market goes to shit you still have a hefty plot to do as you wish with.
You can invest in skills, online courses, or colleges. There are lots of free ones as well. Only a slight risk but by far the slowest payoff.