People say everything has already been explored. They're wrong of course. There are oceans (literally) of places yet to be explored. The deep ocean, outer space, microscopic things, the human brain, and probably others which I'm just not thinking of right now.
With writing... I think it is much harder to find new places to explore in writing. Even the unexplored real places have been written about, in many ways, with many theories. Music is all based on a set amount of notes and yet there are millions of songs. Music also has genres and styles. I don't write music but it seems to be even harder than writing with words. For one thing, we have 26 letters and they work with billions of words.
I think everything (unless it doesn't exist yet) has been written about. Science fiction covers so much, a wide area of imagination and speculation. Non-fiction explains everything under the sun, just search online for "how to..." and there will be something.
So, what can you do when you don't feel there is anything new to write about? Some would say "write it better" but I would say - write it your own way. You have your own life experience, your own ideas and ideals, and you can write things from your own perspective.
If that doesn't help, throw things together and see what you come up with, randomly. Put together ideas and items that don't go together, are unrelated and make it work in some way. It's fun once you start.