If goodness is subjective, then goodness is dependent on the person.
There could be no goodness without people.
Saving humanity from destruction is saving goodness from destruction.

There CAN be objective truth without objective goodness, though.
But that doesn’t make objective truth objectively good.
The truth is often unpleasant, and one’s concept of goodness may hinge on what is pleasant.

However, learning the truth is the best strategy for saving humanity from destruction.
Any argument to the contrary would have to be both LEARNED and TRUE in order to be valid.

If your concept of good does not include maintaining the conditions for maintaining goodness, then your goodness is not sustainable and should rightfully die off.

I believe this is the closest one can rationally come to objective good:
To love the world. To give and receive the truth. To save the world. To protect the people.