"In a mystery, the plot normally centers on a protagonist trying to get to the bottom of a crime. Readers are following a detective as he/she uncovers clues and works toward solving a puzzle. The majority of suspense in mystery novels comes from clues that mislead readers and the anticipation for solving the mystery, rather than a fast-paced plot with extended scenes of violence.
In a thriller, the protagonist is suspended in an almost constant state of danger. These stories create excitement more because of their quick-pace than the building of plot. Unlike mystery, thrillers are not about solving a puzzle, but rather about the pressure of high-stakes scenarios.
Occasionally books will blur the lines between these two genres...." Author Learning Center https://www.authorlearningcenter.com/writing/i-have-an-idea/w/choosing-your-topic/2890/genre-basics---thrillers---article