I don’t think Jonah particularly likes or celebrates Christmas. After all they were not even really a thing till about mid 19th century when Queen Victoria married Prince Albrecht who brought lots Christmas of traditions from Germany.
It’s just some ridiculous modern tradition. It’s just a pointless time where his employees are not working.
Though maybe he could over the years learn to appreciating them for providing some new ways of inflicting trauma on his employees.
He probably gives Christmas postcards wishing Happy Holidays with the family specially to those employees who have no one or who are not really in touch with their relative to remind them how miserable and alone they are.
He organises Secret Santa where he matches the employees in the worst possible combination just so they can stress the whole December about what gift to give on Institute’s Annual Christmas party.