I'm still not seeing any reference to specific violations by X, just some surrounding context and listing of allegations.
The EU has broad discretion to start formal inventigations, but specifically CHOSE to begin litigation against X for specific reasons. I would expect a transparent governing body to provide a litany of information to the public about why they are choosing to take that action. If there is a lack of said information, that would lead one to suspect that information is being purposely concealed and/or that it is a targeted partisan political action.
Alternative hypotheses: the information is published but not reported; the information is reported but you haven't seen the reporting; the information will become available at trial.
Just to clarify, since I believe "partisan" in the US is often meant to refer to one of the two parties, that the EU has several bodies, and the European Commission specifically consists of people nominated by the member countries and do not necessarily come from the same party (to the limited extent that EU-wide parties even exist).
With Musk publicly tearing down lots of the existing moderation and compliance infrastructure and welcoming back highly problematic disinformation actors like Trump and Alex Jones, Twitter seems like an obvious choice?
Yes, it's quite possible twitter platforming certain unsavory people is part of the reason the EU is perusing litigation, but that also somewhat de-legitimizes this action as a legalistic inquiry.
As an aside, the idea of "disinformation" is fundamentally political/partisan because it defines a grouping of conflicting people and ideas. Furthermore, one of the core principles of liberalism is that people in a society will never be able to agree on "hard questions" (i.e. religion, culture, values, economic system) so the government should not take stances on them. If the EU is a liberal institution, then it is totally contrary to be perusing something as arbitrary and difficult as defining what is and isn't "disinformation". They should be leaving that to individuals and private organizations.
Note that they are now starting a formal investigation, whose purpose is to determine whether there are indeed infringements or not.