That's right you can take a look at: ◇ S&P500 Top 50 ◇ S&P500 ◇ S&P Total Market Index
On the mathematical side The number of assets in any portfolio should not be less than 30 in order to reduce the risk of the weighted portfolio and create meaningful statistical significance, and the risks are close to the risks of the total market.
But there are some investors who like to choose a smaller number of assets to increase the return and risk, but they must be blue chips, that is, assets of very large cap, in order to benefit from the market cap bias.
As you know, it is difficult for large companies to fall except in the events of the black swan, and other assets will automatically replace them, but if you deal with the market cap according to set theory, nothing is important.
Anyway, I'm invested in the US market only in the 4 largest companies [Apple - Microsoft - Google - Amazon] with a gold to take advantage of the correlation with the stock market and crypto market
This is considered a safe investment in the long term for me, even with the lack of diversification, because diversification is measured not only in one market, such as only stocks or crypto, but in several markets, even if you own a small number of assets in each market. All that matters is that you trust the investment Confidence only comes from back-testing the investment methodology and always following the same rules Passive portfolios are more reliable and objective in the long run.
Gold - Stocks - Crypto - Bonds - Real Estate ..etc
This is the main diversification in my opinion.