He is actually a big supporter of cryptocurrencies - especially bitcoin!
This is a quote from 2014 - before cryptocurrencies became as well known as today:

Mr. Gates has sung Bitcoin’s praises. Long considered one of the world’s richest men, his eyes light up when he discusses possibilities for the future of Bitcoin technology.

“I think it’s a technical tour de force but that it is an area where governments are going to maintain a dominant role.”
“Bitcoin is better than currency in that you don’t have to be physically in the same place and, of course, for large transactions, currency can get pretty inconvenient.”