'Meaning' within the system - the operation of the process itself. That is well known. And has been explained to you at least twice. That is deterministic. Photons hit some protein. Deterministic. It creates an electrical charge. Deterministic. The charge activates an action potential in a neuron. Deterministic. That releases neurotransmitters. Deterministic. They cross a synapse and activate receptors on the next neuron. Deterministic. And so on.
But you have said that there is something outside the system which is not deterministic which changes physical matter within the system. And you said it was 'meaning'. But you haven't given any idea where this 'meaning' is from, what form it takes, how it is developed, where it acts within the known system, what the effects are, what physical changes are made and when they are made.
I'm not actually sure that you know that this is a form of dualism. And if you had started off with that and suggested something akin to a soul where free will decisions are made - somewhere and somehow, then there would have been nothing to discuss. You would have just claimed that there is something other than the mind for which there is no evidence. But you didn't want to do that. So you dug this rather large hole when you said that wherever this 'something' exists, it acts directly on physical matter within the existing known system.
And not only haven't you said how it does this, you really have no idea how it could do this.