The open-source emulator was previously confirmed to be arriving on Steam this year; however, the development team has since announced that its launch has been "indefinitely postponed" due to reasons regarding the Digital Millennium Copyright Act (DMCA).

The details:

Dolphin's developers announced in a blog post on May 27 that the Steam release of the emulator had been "indefinitely postponed" after Valve informed them that Nintendo had issued a cease and desist citing the DMCA, with Dolphin's Steam store page being removed for the foreseeable future. Nintendo stated in a letter sent to Valve (via PCGamer) that the emulator works by using "cryptographic keys without Nintendo's authorization and decrypting the ROMs at or immediately before runtime" and that it "circumvents" the "technological measure" used for copy protection.
Despite the fact that the blog post stated that Nintendo had issued a takedown request, Pierre Bourdon, the treasurer for the foundation supporting Dolphin, has confirmed that Valve was behind the removal. According to Bourdon, Valve contacted Nintendo about the upcoming release of the emulator on Steam, which prompted Nintendo’s response that it would "violate the DMCA anti-circumvention provisions," leading Valve to remove the emulator's store page.
Dolphin has been around since 2003 and was the first widely available emulator capable of playing actual Gamecube titles before evolving into an open-source project with Wii emulation later on. It has since been made available for platforms other than Windows, such as Mac, Android, Linux, and even the Xbox One and Series X/S, with development continuing to add new features while improving performance. Despite the fact that Dolphin's Steam release has been delayed, those interested in playing some of Nintendo's older titles can still download the software for free from its official website.

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GameCube and Wii Emulator Dolphin removed from Steam