Explanation:

Rambagh, one of the oldest Mughal gardens in India, was established by Emperor Babur, the founder of the Mughal dynasty, in 1528, predating Akbar's reign. It is also known as the 'Garden of Relaxation' or 'Aram Bagh'. In contrast, Jahangir Mahal, located within the Agra Fort, was built by Emperor Akbar for his son Jahangir, making it an establishment under Akbar's patronage. The Agra Fort itself was extensively built and renovated by Emperor Akbar starting in 1565, transforming it into a major Mughal stronghold. 'Akbar Fort' generally refers to forts built by Akbar, such as the Agra Fort or the Allahabad Fort, which were significant architectural projects during his rule. Thus, Rambagh is the only option not established by Akbar.