Exhibit 10.4

JOINDER to the

Registration rights agreement

This Joinder to the Registration Rights Agreement (this “Joinder”) is made this 5th day of February, 2026, by the undersigned, in respect of that certain Registration Rights Agreement (the “Rights Agreement”), a copy of which is attached hereto as Exhibit A, dated as of May 6, 2025, by and between Dune Acquisition Corporation II, a Cayman Islands exempted company (the “Company”) and Dune Acquisition Holdings II LLC, a Delaware limited liability company (the “Sponsor”). Capitalized terms used but not otherwise defined herein shall have the meanings ascribed to them in the Rights Agreement. 

RECITALS:

WHEREAS, the Company desires to appoint Collective Acquisition Sponsor LLC, a Delaware limited liability company (or its designated affiliate(s), the “New Sponsor”) as a party to the Rights Agreement in place of the Sponsor. The undersigned has accepted such offer and agrees to be bound by the binding provisions of the Rights Agreement.

NOW, THEREFORE, for and in good and valuable consideration, the receipt of which is hereby acknowledged, the undersigned agrees as follows:

1. The undersigned hereby agrees to be bound by the terms and conditions of the Rights Agreement as a party thereunder.

2. This Joinder shall be governed by and construed in accordance with the laws of the State of New York without giving effect to any choice or conflicts of law provision or rule that would cause the application of the domestic substantive laws of any other jurisdiction.

IN WITNESS WHEREOF, this Joinder has been executed and delivered by the undersigned as of the date set forth above.

Collective Acquisition Sponsor LLC

Acknowledged and Agreed:

Dune Acquisition Corporation II

[Signature Page to Joinder to Registration Rights Agreement]