At the beginning of 2021, only a niche group of crypto enthusiasts knew what non-fungible tokens (NFTs) were. But by the end of the year, some $25 billion had been spent on NFTs, compared to $94.9 million in 2020, as the speculative crypto asset exploded in popularity—popular enough to be named word of the year for 2021. Though NFTs have been around since 2014, the NFT mania hit the mainstream last March when a digital collage of images, titled “Everydays: the First 5000 Days” by digital artist Beeple (aka Mike Winkelmann), was sold as an NFT for $69 million. The…