Our retirement portfolios consist primarily of stocks and mutual funds that invest in stocks. Some of us own bond mutual funds or bonds and almost all of our cash.
Gold has some advantages as an investment in that it is considered a store of value, which is especially true during times of inflation when the price of gold goes up as other prices rise.
Bitcoin (BTC) is the most well-established cryptocurrency and has the longest track record. In addition, Bitcoin has more major financial institutions involved leading to a measure of respectability and regulatory outline.
This approach is a viable and accepted way to millionaire status, as illustrated by many millionaire interviews. You need some capital to invest in rental properties, and there are risks.