@giuliovialetto this very much looks like the Python configuration is not up to date. I am planning on updating the examples and writing a proper article about the setup of the KNIME deep learning environment which still is somewhat confusing sometimes and constantly evolving it seems
What I would suggest in the meantime is reading about KNIME and Python and conda in my article. Then I would recommend resetting the mentioned workflows and see if the environment propagation would build the correct python environment (make sure to use the one for your operating system):
A condensed version about what to do to setup KNIME and deep learning is here though it is not a fully articulated set of instructions (working on that):