Charles Hartshorne claimed that Charles Sanders Peirce introduced the idea that freedom applied to all creatures:
But Peirce took one more step. He generalized this so that not just human beings make their own decisions but all the animals do and all the creatures do in some degree. They have a very humble kind of freedom compared to ours. We have more freedom and God has supreme freedom....Peirce was pretty close to the first philosopher in the world who generalized the idea of freedom so that it applied to all the creatures....
Hartshorne and Paul Weiss edited Peirce's collected papers for the Department of Philosophy at Harvard.
Peirce wrote an essay "The Doctrine of Necessity Examined" which presented a view opposed to determinism, "necessitarianism" as he called it, which also confirms that he may have held positions similar to those Hartshorne described.
Let's consider the question I posed earlier: Are there philosophers who have considered freedom of choice or free will for agents more generally, not only for those agents that are considered "rational"?
The answer is yes. Such a view was likely held by Charles Sanders Peirce.
A New Worldview_An Interview with Charles and Dorothy Hartshorne, Center for Process Studies https://www.youtube.com/watch?v=A4CLEpIY0hY&list=PL1HA-Ghi6Kv1WmMb4rWQCn9yRgJ5w6uoN&index=2
Peirce, C. S. "The Doctrine of Necessity Examined", The Information Philosopher http://www.informationphilosopher.com/solutions/philosophers/peirce/doctrine_of_necessity.html
Peirce, C. S., & Buchler, J. (1955). Philosophical writings of Peirce: Selected and edited, with and Introduction, by Justus Buchler. Dover Publications.