Do you mean something that has no agent, or something self-subsisting that has no agent?

If you mean the first, nothing precludes each of the attributes, as well as the essence, from being a necessary existent under this definition. No proof establishes that there cannot be multiple necessary existents under this definition, just as no proof establishes that there cannot be multiple beginningless things under this definition. What the proof establishes is only that there is no god but Allah, and that Allah, the Lord of the worlds, is One, without partner. This is the monotheism established by revelation and reason.

As for negating the attributes and calling that monotheism, this contradicts revelation and reason.

If by “necessary existent” one means something self-subsisting that has no agent, then the essence would be necessarily existent: it would be necessarily existent together with its attribute, whereas the attribute alone would not be necessarily existent.

If the need of the attribute and that which possesses it for one another means that they are inseparably linked, this is to be affirmed. It does not follow that either is an effect of the other, for mutually correlative things are inseparably linked, yet neither is an effect of the other. If, however, what is meant is that one is the agent of the other, then need in this sense is to be denied. This is the first alternative: neither needs the other.