iOS uses machine learning, which is a learning feature from your usual functions, data and folders used. If you change the way you use the data it automatically will get itself changed over a time period
Settings > Mail > Siri & Suggestions [enabled?] Siri may learn from and make suggestions based on how you use an app.
However you may....
- To turn off Siri Suggestions, go to Settings  > Siri & Search, then turn off any of the following:
- Suggestions in Search
- Suggestions in Lookup
- Suggestions on Lock Screen
For a specific app, tap the app, then turn off Show Siri Suggestions.
Your personal information—which is encrypted and remains private—stays up to date across all your devices where you’re signed in with the same Apple ID. As Siri learns about you on one device, your experience with Siri is improved on your other devices.
- Siri is designed to protect your information, and you can choose what you share. To learn more, go to Settings  > Siri & Search > About Search Suggestions & Privacy.