Power of Attorney for Kathleen S. McAllister

This filing contains a Power of Attorney granted by Kathleen S. McAllister, a director of HMH Holding Inc., to Thomas W. McGee, Dwight W. Rettig, and Cindy Nichols. This authorization allows the appointed attorneys-in-fact to execute and file necessary documents with the SEC, including Forms 3, 4, and 5, on behalf of Ms. McAllister. These forms are required for reporting securities transactions and ownership as per Section 16 of the Securities Exchange Act of 1934. The power of attorney also grants the attorneys-in-fact the ability to obtain information regarding the company's securities from third parties and to take any other necessary actions beneficial to Ms. McAllister. The authorization remains in effect until Ms. McAllister is no longer required to file these forms, revokes the power of attorney in writing, or the attorneys-in-fact are no longer associated with the company. The document was executed on August 21, 2024.