Is it permissible to give an in-kind gift (a computer) from the company's account to the owner's representative after the contract has been signed, knowing that he pressured the contractor to lower the project's value, and is this considered among the types of "ghulul" (misappropriation/embezzlement) mentioned in the Hadith?

The agent of the owner must seek the best interest of his principal. What the agent did, bargaining to get the best offer for the owner, is the core of his work for which he receives a wage. He has no right to demand anything, as this demand of his falls under the general meaning of the hadith: "Gifts to workers are ghulul (ill-gotten gain)." Narrated by Ahmad. It is not permissible for you to give him anything because what is forbidden to take is forbidden to give.