https://wccftech.com/macos-big-sur-with-new-ui-ipados-hand-writing-improvements-and-more-leaked/

In a number of last minute leaks leading up to WWDC20, leaker @l0vetodream has revealed details for several product updates to be announced at the event. These include macOS 'Big Sur' name with a redesigned user interface, updates for Safari, tvOS update with HomeKit support, watchOS update with sleep monitoring, and much more.

The name of the upcoming major macOS update will be 'Big Sur'. Ever since Apple stopped using cat names for OS X releases, it has been using names of various locations in California. Keeping up with this tradition, it seems possible that Big Sur, a mountain region in the central coast of California might be the name of the next macOS release.