The root cause of an error is: /usr/bin/python3.9: No module named py_compile.

This will prevent python3 packages from installing as the dpkg errors out during configuration.

A more complete error example, will look something like this:

Setting up python3.9-minimal (3.9.2-1) …
/usr/bin/python3.9: can’t open file ‘/usr/lib/python3.9/py_compile.py’: [Errno
2] No such file or directory
dpkg: error processing package python3.9-minimal (–configure):
installed python3.9-minimal package post-installation script subprocess return
ed error exit status 2
Errors were encountered while processing:
python3.9-minimal
E: Sub-process /usr/bin/dpkg returned an error code (1)
…
/usr/bin/python3.9: No module named py_compile

Regardless of the package name, missing the py_compile will give plenty of issues. Here comes an easy fix.

As a user root user (sudo su):

wget https://raw.githubusercontent.com/python/cpython/3.9/Lib/py_compile.py -O /usr/lib/python3.9/py_compile.py

Verify that the file exists in the correct location:
ls /usr/lib/python3.9/py_compile.py

Output should return:
/usr/lib/python3.9/py_compile.py

Reconfigure dpkg as a root or sudo:

sudo dpkg --configure -a

Output should return something like this:

Setting up python3.9-minimal (3.9.2-1) …

After this, python3 dpkg related stuff should be ok and installations should just work.