Abraham Maslow seems to suggest that while purpose should be an overarching theme of one’s life, a mental state such as happiness couldn’t be the purpose.

I agree that purpose does not always have to be a mental state (a purpose is not always a core desired mental state). Purpose becomes what people choose it to be. But I have argued for the benefits of rephrasing our purpose as a mental state (align purpose with a core desired mental state).

I still believe on my conclusion that what we ultimately want is to be in a particular mental state, and so ginhawa or happiness are still viable purposes. What I’m understanding from the research, however, is that even if Ginhawa or Happiness is the ultimate purpose, pursuing it by focusing on it may not be the best way to feel it as it is simply a by-product of pursuing lower level goals.

A good metaphor to understand this is meditation. Some people do meditation to find peace of mind or achieve altered mental states. However, they fail to achieve these mental states if what they “focus” on is the mental state. They only achieve this by pursuing a lower-level goal. In this case, counting one’s breath or uttering a mantra.

In a similar way, Happiness and Ginhawa or other core desired mental states are still viable purposes. But we can't experience them by "focusing” on them. We achieve them by focusing on the practices that we can do every day to achieve them or to cultivate our capacity to experience more of them.

This is so similar to James Clear’s insight (set it and forget it) and other insights like “process over product,” “the journey is the reward,” and “focus on what you can control.”

References

Clear, J. (2018). Atomic Habits: An Easy & Proven Way to Build Good Habits & Break Bad Ones (Illustrated edition). Avery.

Kaufman, S. B. (2020). Transcend: The New Science of Self-Actualization. TarcherPerigee.