apt-get python not installable but it is

On Ubuntu, trying to install a deb-file (armory 0.96.5), I get the error:

depends on python (>= 2.6), but it is not installable.

Well, it already is installed and just typing python --version in the command-line shows me it’s version:
Python 3.13.7

Why does it not find my python-version and how can I tackle this?