macOS gives you a choice to download whatever version is currently available of the macOS you need.

macOS Big Sur is the 17th major release of macOS, Apple Inc.'s operating system for Macintosh computers, and is the successor to macOS Catalina. It was announced at Apple's Worldwide Developers Conference on June 22, 2020, and was released to the public on November 12, 2020.

macOS Catalina is the sixteenth major release of macOS, Apple Inc.'s desktop operating system for Macintosh computers. It is the successor to macOS Mojave and was announced at WWDC 2019 on June 3, 2019, and released to the public on October 7, 2019.

macOS Mojave is the fifteenth major release of macOS, Apple Inc.'s desktop operating system for Macintosh computers. Mojave was announced at Apple's Worldwide Developers Conference on June 4, 2018, and was released to the public on September 24, 2018.

macOS High Sierra is the fourteenth major release of macOS, Apple Inc.'s desktop operating system for Macintosh computers. macOS High Sierra was announced at the WWDC 2017 on June 5, 2017, and was released on September 25, 2017. The name "High Sierra" refers to the High Sierra region in California.

macOS Sierra is the thirteenth major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers. The name "macOS" stems from the intention to uniform the operating system's name with iOS, watchOS, and tvOS.

OS X El Capitan is the twelfth major release of macOS, Apple Inc.'s desktop and server operating system. It focuses mainly on performance, stability, and security.

OS X Yosemite is the eleventh major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers. OS X Yosemite was announced and released to developers on June 2, 2014, at WWDC 2014, and released to public beta testers on July 24, 2014.

Anyone with a Developer account might be able to download even older versions here.