According to the Steamworks documentation, blockchain games and NFTs are now prohibited on the platform.

This change was noticed by NFT developer SpacePirate io, who stated that the move was made because the firm does not want to allow games that give players real-world stuff.
Community: A few minutes ago, we were notified that @Steam will be kicking *all blockchain games* off the platform, including Age of Rust, because NFTs have value. Behind the scenes, we've had good communication and have been upfront with Steam. #blockchaingames #NFT
— Age of Rust (@SpacePirate_io) October 14, 2021
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On the other hand, Epic told The Verge that it is open to the notion of games using either NFTs or cryptocurrency structures. They are open to the idea, but they recognize that there will be some limits, and they are willing to collaborate with people in this industry.
Epic Games Store will welcome games that make use of blockchain tech provided they follow the relevant laws, disclose their terms, and are age-rated by an appropriate group. Though Epic's not using crypto in our games, we welcome innovation in the areas of technology and finance. https://t.co/6W7hb8zJBw
— Tim Sweeney (@TimSweeneyEpic) October 15, 2021
According to Epic, the games would also have to follow banking regulations, explain how the blockchain works, and have suitable ages. They also stated that crypto would not be accepted as a form of payment on the Epic platform.
Valve has yet to comment on the situation, so stay tuned for future updates like these.
Source: The Verge, SpacePirate, Steamworks Documentation