Some millionaires have only one form of income and some millionaires have more than one form of income.
You can become a millionaire by several ways such as through Real Estate, Investing, Investing in Oil wells, running a popular Youtube Channel, owning large stores, owning a bunch of gasoline stations.
Think Tom Love from Love's gas stations he's a billionaire and makes money with no work now through all the gas stations he owns.
You could buy stock in Love's Gas stations and make a lot of money.
Most millionaires have more than one bank account to protect their money in the event of a bank failure.
If you want to become a millionaire it's possible but most times it takes a few years or longer of hard work to become a millionaire.