An EU Inc. has a registered office in one member state but can operate across the 27. The question of where it is tax resident, and how that residence interacts with permanent-establishment tests, profit attribution, and CFC rules, is among the harder pieces of the dossier.
The proposal generally follows the principle that tax residence is determined by national rules of the member state of registration, subject to applicable double-tax treaties. This preserves national tax sovereignty but leaves substantial scope for interpretation, particularly where management and control sit in a different member state.
This page tracks each country's current tax-residence test for companies (place of effective management, place of registration, hybrid), any guidance issued by national tax authorities on EU Inc., and signals from the Commission and Council on harmonisation. Practitioner commentary is heavy here because corporate tax lawyers see the file as one of the most uncertain.