Philosophy, law, and religion have been grappling with that question for a long time but I’ll take a swing.
For me personally, individual freedom is the highest good. Anything that increases it is moral and anything that decreases it or decreases it for others to increase your own is immoral.
"Morality" (from whatever direction it is studied/theorized from)
Is behavior that promotes/provides cohesion for a group.
Different groups/cultures arrive at differing concepts and systems.
This is why pure ideologies that redefine morality in the context of a larger group tend to have a hard time.