LONDON—Bitcoin close to $70,000, “memecoins” worth billions of dollars, a blockbuster Wall Street listing and a sweeping Chinese crackdown: 2021 was the wildest yet for cryptocurrencies, even by the sector’s volatile standards. Digital assets started the year with a stampede of cash from investors large and small. And bitcoin and its kin were rarely out of the spotlight since, with the language of crypto becoming firmly entrenched in the investor lexicon. Here is a look at some of the major trends that dominated cryptocurrencies this year. 1. Bitcoin: Still Number 1 The original cryptocurrency held its crown as the biggest and most well-known token—though not without a host of challengers biting at its heels. Bitcoin soared over 120 percent from Jan 1. to a then-record of almost $65,000 in mid-April. Fueling it was a tsunami of cash from institutional investors, growing acceptance by major corporations such as Tesla Inc and …