AsciiDoc3 is of course written in Python3 - at the time of writing you need 3.7 or higher.
To use all the features of AsciiDoc3 you need a bunch of third-party tools like Apache’s FOP, GNU-highlight, lxml and so on … And perhaps Python software like dblatex and lilypond?
But be careful, these two have shown a little delay in terms of migrating from Python2 to Python3: Ubuntu LTS 20.04 still runs with versions which depend on Python2.7.
But these times are gone, in the meantime all stuff was migrated to Python3. You can run everything around AsciiDoc3 without the outdated Python2.7.

Keywords: AsciiDoc3 Python3 Dependencies