mpy-cross-v5 breaks when installed on python3.8

It installs fine through pip, but then breaks at runtime with an error just like this one: https://stackoverflow.com/questions/75202610/typeerror-type-object-is-not-subscriptable-python

Probably it should refuse to install at all on py3.8 . (Py3.8 seems to be the newest available in Ubuntu 18.04 LTS)