Stop my phone from messaging "Good morning" and "Good afternoon" and "You have a new memory" to me
“Good Afternoon” is an example of “Siri Suggestions” and they can be turned off in Settings under “Siri &amp; Search”.
The feature’s goal is to surface content/actions that it thinks will be useful to you in that moment.
Possibly this will get more useful over time, given that your previous OS may have not been recording how you use your phone.

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To turn off notifications about suggested Memories in Photos, visit Settings - Notifications - Photos - Memories: