The EU interfering directly with domestic politics of member states by for example banning political parties would, safe to say, not be well received.
Leyen is completely correct, and for sure the EU needs to work to build resistance in Europe against foreign propaganda, but it's not so straightforward for the EU to intervene in these things. It remains the responsibility of the individual member states, and one might reasonably argue it is better left that way.
That said, when the EU considers banning vectors of foreign surveillance, that is one thing that they can do and that they seem to consider. It's just a fine line between taking action and overstepping. European countries tend to cling to some degree of sovereignity, especially in questions of national security.