Looks like Gutenberg have got a new experimental feature that allow theme authors to create Global Styles variations.
All you have to do is to create a new directory styles under the root of
your theme and place a new
.json file in there.
The schema of the file is exactly the same of the theme.json except for the property title which will be the name used within the browse styles Section.
Take Twenty-Twenty Two Theme as an example since the theme already includes three styles variations.