Check the profiles of the girls which you can find from the heart icon at the top. The story events are listed below the hearts and on the right are all the events you can do with them. For example if Prim's chat event says available then you can see more content. If it said unavailable then you need to progress the main story to unlock more. And if it said "work in progress" then that is everything for that event for the current update.
Yeah some will be training events and some could be shower events. Prim and charlotte shower in the morning while maxy and mary are during the evenings. Yui is at the beach at noon at you can have an interaction then too. Majority of the scenes though are from the main story or training events.
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Here Stawer posts progress reports and will add hints for scenes in a future technical update not the public release (so it doesn't bring confusion). Though if there is any other things you are missing I would gladly help you