Login to your Gmail from browser.
Click gear icon on top right > See all settings
- Undo Send: 30 seconds (Not necessarily a privacy feature but might come in handy)
- Images: Ask before displaying external images
- Grammar: Grammar suggestions off
- Spelling: Spelling suggestions off
- Autocorrect: Autocorrect off
- Smart Compose: Writing suggestions off
- Smart Compose personalization: Personalization off
- Smart Reply: Smart Reply off
- Smart features and personalization in other Google products: Off