Maybe my brain has rotted from paying a bit more attention to privacy language than the average person, but IMO in this case it's fairly clear to me that using your activity “to personalize your experience across Workspace” does not mean using it for training Gemini. The “personalize” means it's for training the recommendation/categorization systems for you, like which emails get marked as "important" or not (the settings at https://mail.google.com/mail/u/0/#settings/inbox).

(In some very broad sense I guess critics could call this “training AI” as there's an ML system somewhere whose parameters associated with your account get updated, but I think we can all agree this is not what we think of as “training AI”, i.e. going into a cross-user dataset for training Gemini or whatever.)

(I guess what Google should do, and should have done years/decades ago, is create a fixed set of categories of how your data can be used (aggregate statistics, training Gemini, personalization…) and use the same language across products, legal, everything.)