Unless explicitly promised otherwise, the assumption is always that anything being passed to a LLM API may be retained for various reasons. That’s the expectation that’s been set by the industry.
"We do not use your Workspace data to train or improve the underlying generative AI and large language models that power Gemini, Search, and other systems outside of Workspace without permission."
https://support.google.com/docs/answer/14615114?hl=en
Edit: I believe that this "without permission" caveat refers to experimental things like Workspace Labs where you have to give them that permission if you decide to join.
https://support.google.com/docs/answer/13447104?hl=en#labs-o...
I'm not sure whether there are any other beta programs that require these permissions.