For decades now, Apple has been using the version 10 on its operating system. First it was called Mac OS X, then it was simply OS X, and then the Cupertino firm moved on to macOS. But when it started calling it macOS, it really stopped making the version numbers so public. They were there, but no one said them out loud. macOS 10.15 Catalina was simply macOS Catalina.
Yesterday at WWDC 2020, Apple introduced this year's macOS update, called Big Sur. Some savvy viewers noticed that this time around, it's actually version 11, even though Apple never explicitly said it. While it might have been possible that the company was using some internal version with a different number, after installing the beta, it's clear that Big Sur is macOS 11.
It's unclear how Apple is going to do its versioning going forward. Next year's version could very well be macOS 11.1, although it seems more likely that it will be macOS 12. There doesn't seem to be anything specific about this release that would indicate such a major change that it's a whole new generation. Apple probably just wanted to change up the way it numbers releases.
It does have ARM64 support for the first time, as the company is moving to its own ARM processors for the Mac, ending its partnership with Intel over the next two years. But still, Mac OS X, in its time, originally supported PowerPC and survived the shift to Intel.