1. Real estate
2. Cryptocurrencies
3. Business .
Which one would you choose from these and why?
Each of the investment opportunities you listed above have their strength and their weaknesses so it'll be difficult to depend on only one. Real estate is a secure way of investing as house that you buy to rent or resell can always be sold on the market and you don't have to look for buyers yourself as real estate can sell itself and make you your money back. Business are long term investment as they will not only give you one time profits but forever income provided the business is running.
Cryptocurency is the quickest way to making money legitimately currently but it also has the disadvantage of having so many scam projects that you can get scammed easily investing in cryptocurency. If I had half a million I'll divide the money and invest in the three.
Of course, if you wanted passive income, then go for real state. You just have to shell out huge money in the beginning, fix the property and have it rented and you will be set for years.
For crypto, there are a lot of ups and downs, bear and bull market, and you need to be mentally though and continue to buy and hold and wait for the next bull run to sell.
For Business, hard work of course, you have all the time in the world but you have to focus on it and how to bring more money into your business.
In short, there are a lot of challenges to be filthy rich.