There are two types of happiness. With the temporary kind we feel happy when we enjoy something like a good meal, a film, a day out bushwalking with friends. . . . and yes, that is subjective. Someone will be happy bushwalking, whereas someone else won’t be. Some people enjoy eating mangos; others don’t. Our species benefits when we get pleasure in diverse ways. (If someone in a tribe gets pleasure from studying the stars, while another gets pleasure from weaving baskets, and yet another gets pleasure from gardening, then navigation improves, baskets are made, and food is grown. That tribe will do better than a tribe consisting solely of star gazers or basket weavers.)
So yes, our species evolved to have diverse interests, and therefore, diverse pleasures. That is why temporary happiness is subjective.
However, core happiness, (the general day-to-day feeling of well-being), evolved as a reward for engaging in long term beneficial behaviours. Long term beneficial behaviours don’t require diversity. Long-term behaviours are more pervasive and more uniform. For core happiness we have universal propensities, which means that it’s not subjective.
In short, temporary happiness is subjective; core happiness isn’t.