The person that is able to act is an aggregate of matter. If I am only a mind, a soul, then it is possible to think but not to act. Action involves the mind “intra-acting” with the body.

Does the self have an essence or is it a relationship?

The self is not the mind only. While the mind could be essential, the self isn’t. The self is ever-changing.

Then there is that statement: nothing is truly independent.

The mind cannot exist without a body. Self cannot exist without both mind and body.

Something could be metaphysically exclusive but will not exist without the others.