There are explicit data retention contracts for Workspace (including Gemini transcription) and Google claim this data is never used for training or human review, so this is fairly baseless.

This gist is specifically about the consumer version of Gemini used in Gemini Apps. Basically if you connect your consumer Gemini (which always sends stuff to the training pipeline) to your personal Google Apps account, it gets tools that it can invoke to read your Google Apps data, which then might appear back in your consumer Gemini transcripts that are getting sent to the training pipeline.

Doing this is a stupid product move from Google (per the usual) because it confuses their enterprise customers into thinking Really Bad Stuff like this is happening.