Open Snapchat, go to Settings → Notifications → Story Notifications, and turn off “From Everyone” or disable story notifications for non-friends. This stops alerts from people you haven’t added while keeping notifications from friends active.
To stop Snapchat story notifications from non-friends, open Snapchat Settings, go to Notifications, tap Stories, and turn off “Creator Stories” or “Public Stories.” This ensures you only receive story alerts from your friends.