A conflict can be rooted in the main plot, it can be rooted in a relationship between characters, or it can be both. Here are a few strategies for creating a new conflict in a scene.
Beats come in four types: action, reaction, setup, and deepening. A beat can only ever be one type. Most scenes are dominated by 1-2 types of beats, though they can easily include all 4.
Stories are a combination of scene & summary. Even the shortest story contains at least one scene or summary. A scene is when a small span of time is covered in great detail; a combination of what characters say, the actions they take, and any relevant details. A summary is when a large span of time is covered in only a few words.
A good mystery is all about the question. If the protagonist is a criminal then the question is “how will they accomplish the difficult task”. If the protagonist is a detective then the question becomes “how did they do it”. In both cases the beginning establishes how difficult the task is or was, then spends the rest of the story gradually dropping hints and clues, giving audiences the chance to try and solve the mystery. The key is to carefully manage information so that audiences feel like they have a chance, but don’t solve the mystery before the end of the story. Many mysteries use comical side plots to break up what can be a dry main story.