Sotheby’s sale was a far cry from the $69 million paid at Christie’s last month for a single NFT by Mike Winkelmann, who goes by Beeple, but the broad bidding for Pak’s “The Fungible Collection” series may be a sign that cryptocurrency collectors are seeking out complex, wryly conceptual NFTs by digital artists with lengthy track records online. At boutique auctioneer Phillips, bids have already topped $2.4 million for “The Replicator,” an NFT by another digital artist who goes by Mad Dog Jones. That sale ends April 23.

In the Sotheby’s sale, top prices were paid for Pak works that showcased a level of market savvy and gamelike complexity that would be impossible with a canvas or sculpture in real life. “The Switch,” which sold to California cryptocurrency investor Damian Medina for $1.4 million, is a digital image of a rotating, black-and-white geometric shape—but its bigger appeal lies is the fact that the entire work is designed to change form if its new owner ever decides to try it. Once switched, it can’t be undone, though, creating an element of suspense.

Another work, “The Pixel,” sold for $1.4 million and elicited bids from many top NFT art collectors in part because its medium-gray monochrome represents a single pixel, the building block of digital imagery. The competition winnowed to three bidders who spent more than an hour and a half dueling it out in small increments—lobbing some bids as low as $50—before before crypto-art collector Eric Young won the work. At one point, the artist acknowledged the protracted match by tweeting images of snails and calling it a “pixel scale bidding war.”

Another work in the sale, “Equilibrium,” looks like a deceptively simple white orb—the artist typically sticks to minimalist, grayscale hues—but it unpeels like an onion with different components. Offered in an edition of four, one version called “The Cryptographer” was given to an obscure Dutch artist named Mathijs Vissers, who solved a puzzle attached to the work. Another version, “The Hunter,” was given to whichever collector paid the most to buy an older piece by the artist offered on a different site during the run of the Sotheby’s sale.

Pablo Rodriguez-Fraile, a Miami mathematician who said he owns 60 of Pak’s works, said he’s been fielding calls all week from blue-chip painting collectors curious about this digital upstart. “It’s an exciting, historic moment for digital art, and Pak is part of a profound social experiment,” Mr. Rodriguez-Fraile said. “He’s art history.”

Pak maintains a cryptic persona and has declined through a Sotheby’s spokesman to confirm any biographical details, other than to prefer the pronouns “they/them.” It also remains unclear if Pak represents an individual or a group of designers.

Pak’s auction will likely elevate the artist’s profile in traditional art circles. Until now, the artist was best known for The Archillect, a social-media feed Pak designed to be run and curated by an algorithm of artificial intelligence. Even so, Pak is widely known in digital design circles for creating sleek, wryly conceptual artworks that explore ideas about value and ownership, and this latest series, “The Fungible Collection,” explores the NFT world’s market aspects in fresh ways.

Max Moore, the Sotheby’s specialist overseeing the sale, said, “Some people think there’s a stigma to buying a JPEG, but once you dive into the technology, there is a conceptual sophistication that’s not possible anywhere else in art,” adding, “With Pak, we’re just scratching the surface.”

Mr. Moore said the house broke with auction convention by allowing the artist to sell an open edition—or a conceivably endless supply—of “Cubes,” and nearly 20,000 cubes sold for $500 apiece during a 15-minute time slot on the sale’s first day. That amounted to nearly $10 million on Monday alone. Similar time slots were opened on Tuesday and Wednesday—attracting so much traffic on Tuesday that Nifty Gateway’s site temporarily bogged until the glut of credit-card transactions could get processed. All in, the artist sold 23,598 cubes to 3,080 people for a combined $14 million.

After the cube sale opened, Pak added another twist by saying these NFTs could be “burned,” or destroyed and thereby converted from unique art tokens back into the artist’s newly created cryptocurrency dubbed ASH—a crazy-eight value loop that could befuddle traditional collectors but appeal to cryptocurrency veterans accustomed to plying their fortunes into tradable digital coins.

Colin Goltra, a Manila-based executive at a cryptocurrency exchange said he bought cubes and followed the sale, and the artist, closely. He says, “Pak is our Picasso.”

Write to Kelly Crow at kelly.crow@wsj.com