Yes, in general, a consortium agreement is required for Horizon Europe projects. According to article 7 of the Horizon Europe Model Grant Agreement, a consortium agreement is required for a Horizon Europe project. Below the details and references.

References:

AMGA Article 7 – Beneficiaries

The beneficiaries must have internal arrangements regarding their operation and co-ordination, to ensure that the action is implemented properly.

If required by the granting authority (see Data Sheet, Point 1), these arrangements must be set out in a written consortium agreement between the beneficiaries, covering for instance:

• the internal organisation of the consortium
• the management of access to the Portal
• different distribution keys for the payments and financial responsibilities in case of recoveries (if any)
• additional rules on rights and obligations related to background and results (see Article 16)
• settlement of internal disputes
• liability, indemnification and confidentiality arrangements between the beneficiaries.
  The internal arrangements must not contain any provision contrary to this Agreement.

For linked actions, the beneficiaries must have arrangements with the participants of the other action, to ensure that both actions are implemented and coordinated properly.

If required by the granting authority (see Data Sheet, Point 1), these arrangements must be set out in a written collaboration agreement with the participants of the other action or, if the consortium is the same, as part of their consortium agreement, covering for instance:

• the internal organisation and decision making processes
• the areas where close collaboration/synchronisation is needed (e.g. on management of outputs, common approaches towards standardisation, links with regulatory and policy activities, common communication and dissemination activities, sharing of information, access to background and results, etc.)
• settlement of disputes
• liability, indemnification and confidentiality arrangements between the beneficiaries in both actions.
  The arrangements with the participants of the other action must not contain any provision contrary to this Agreement.