Not just on this project, but I've seen a few more not moving past 3.8 for support and I don't quite get why that's been happening. Did something happen on 3.9 or later that didn't caught my eye?
One reason could be that 3.8 is the last version to support Windows 7, which (despite EOL) is still widely used.
Maybe it's because Ubuntu LTS, currently 20.04, is on 3.8.
Somewhere around there is when python changed the collections.abc stdlib naming convention from a warning to a fatal error. This means that code could work fine in 3.8 ish and refuse to run on 3.9+.
That probably explains why when I try to use subuser commands (python3.10 installed on the system) it complains "AttributeError: module 'collections' has no attribute 'Mapping'"
A bit of a pain. But to be fair, this import was deprecated since python 3.3, released almost 10 years ago.