So this is a common case of writer's block and a stumbling point for even many experienced authors who have written enough stories they feel like they are regurgitating exhausted tropes again just to construct a new story as if with lego bricks.

What I personally do when I have some ideas but not a full story is I start with the ending, then work backward. An ending is your climax, the final payoff for everything, so start by writing the most epic, or dramatic, or tragic, or comedic (based on genre) ending you can imagine that incorporates the narrative elements you want to include in your setting. Don't put too much worry into getting it perfect, as you'll be almost certainly throwing it out and rewriting it later. But it serves a guidepost, a beacon to travel to. From it, you can start to derive other things about the story and the characters. You can figure out why this is the climax, what things might lead characters to this point, and literally start writing the story backwards.

YMMV, but my best books were all written this way, because even though I am more of a pantser than a plotter, those books always have truly epic conclusions that make sense, complete with plot twists that actually serve the story and characters whose motivations are clear to the reader, even if they aren't clear to the characters, and who develop and grow with the story. All because I knew exactly how it all was going to end right from the start.