Again, without knowing the exact story, possible themes could be despair. If it's a story about a difficult time, despair would likely be a big part of it.
One possible theme could be hope. If it's based on a true story, even during the darkest times, there must be some glimmer of hope that the characters hold on to, just like in real - life difficult situations.
I'm not sure specifically which 'the endless night true story' you are referring to. There could be many stories with such a title or a similar concept. It could be about a long and difficult period in someone's life, like a struggle that seemed to have no end.
Well, 'Endless Summer' is typically not based on real events. It might draw inspiration from various sources but is mainly a fictional creation to offer an enjoyable reading experience.