if an investor can hold a portfolio of almost infinite number of assets $($N is infinity$),$ what happen?

$1.$ Average variance of individual stocks will almost not matter to the portfolio level variance

$2.$ Covariance becomes almost the main risk that drives the portfolio level variance

$3.$ People will almost not care about stock level risk, but instead care about systematic risk that makes every stock comove with each other $($covariance$)$ such the Covid shock

$1$

$2$

$3$

$2$ and $3$

$1,2,$ and $3$