Which macOS version was the first to run on Apple Silicon (M1) Macs?

The first macOS version to run on Apple Silicon M1 Macs was macOS Big Sur.

Apple released macOS Big Sur, version 11, on November 12, 2020, during the company’s transition from Intel processors to its own Apple silicon architecture. The first M1 Macs were the late-2020 MacBook Air, 13-inch MacBook Pro, and Mac mini. They shipped with Big Sur, which could run natively on both Intel-based and ARM64-based Mac hardware.

Big Sur was built to ease the transition. Developers could create Universal 2 apps containing both Intel and Apple silicon code, while Rosetta 2 translated many Intel applications so they could continue running on M1 systems. On Apple silicon Macs, Big Sur could also run many iPhone and iPad apps without conventional Mac ports.

The answer is not Catalina: Catalina supported Intel Macs and was the final macOS release before Apple silicon Macs reached consumers. Monterey and Ventura came later, adding features and supporting newer generations of Apple silicon. Big Sur also marked a major naming milestone, since Apple advanced macOS from version 10.x to version 11 for the first time since the early Mac OS X era.