This is kind of like asking which company with an under $20M market cap can enter the same league as Apple, Microsoft, JPMorgan and IBM. No one knows the answer to this type of questions, aside from the insiders behind one of those under 20M cryptocurrencies.
At this point, you should scroll below to the 369th position on Coinmarketcap to find the cryptocurrencies under 20 million. CargoX, ProChain, Linda, BLUE, Florin Coin - sound familiar? I don’t think.
This doesn’t mean that it’s impossible to jump from $20M to above $100M - this is actually what the crypto market is all about. But guessing which of those might do it first is quite impossible.
There are tokens that explode out of nowhere. For example, U.CASH gained thousands of percentage points immediately after its launch.
There are more stories like this, but jumping from $20M to $2 billion is not an easy achievement.
Why would one invest in a token that has under $20M market cap? On the contrary, you should avoid these coins because they are prone to pump and dumps - a process in which the insiders promote the token on social media channels and inflate the price artificially, after which they sell their tokens for fiat money or other coins and leave the coin to collapse.
Investing in some coins in the top 100 or even top 200 would be a much better approach. If the cryptocurrency market cap is under $20M, it doesn’t mean its token is necessarily cheap. You can buy under $1 tokens of projects that enter the top 100 and still have much room for growth.
So - it’s difficult to give a precise answer.