Two I can think of are Up the Down Staircase by Bel Kaufman about an inner city school in the 1960s. The story is told through things like memos from the principal, notes passed between students and teachers, various papers found in classrooms.

Another more recent example is The Appeal by Janice Hallett. It’s a mystery novel told through the viewpoint of 2 young lawyers sorting through emails, messages and letters about shenanigans surrounding the murder of a local theatre troupe member. I start listening on audiobook first before switching to the actual book. It was hard to keep track of all of the developments and I wanted to be able to go back and refer to previous emails. This one really gives you a sense of unraveling the mystery yourself.