Until now, the alpha releases of Plone 6.1 supported five Python versions: 3.8 through 3.12. In the next alpha we will drop 3.8 and 3.9. So 6.1 will support 3.10, 3.11, and 3.12. This was agreed during the meeting of the Plone Steering Circle last week. This is a meeting of Plone team leaders.
This means less burden on maintainers within the Plone community, like the release team and A/I team (including testing), and opens up the possibility for Plone core developers to use some more recent features. For inspiration, here is the Python document explaining what is new in each Python version:
See what's new in 3.9 and 3.10 for what we can now use in 6.1 that was not possible earlier, for example the zoneinfo module and structural pattern matching (match/case).
If you must use an older Python version, you can stay on Plone 6.0, which will support each Python version until it runs out of security support from the Python community. For Python 3.8 this is October 2024, for Python 3.9 this is October 2025. See https://www.python.org/downloads/.