If you choose to share your suggestions with the Journal application, you are in control of your entries. When the phone is locked with an access code, entries in the Journal application are encrypted. If you have default two-factor authentication and an access code, all Journal entries are end-to-end encrypted when stored in iCloud, so even Apple can't read them. In addition, you can choose to enable secondary authentication and lock the Journal app with the device's access code, Face ID or Touch ID.
You can control what suggestions are shared with the journaling apps that use journaling suggestions by selecting the moments that are meaningful to you and adding them to the application. Tips for keeping a journal are designed to protect your information, as they allow you to choose what data to use to make suggestions and what you want to share with journaling applications. Your decision to turn off all suggestions will apply to all journaling applications that use journaling suggestions. But it's very easy not to use the Journal app or lock your Diary so that only you can access it with Face ID, Touch ID or your access code.
The Journal application allows users to write down their thoughts and feelings, as well as reflect through a journal.