No.
It's not possible to export items with a one-to-many relationship in a flat CSV (or Excel) format.

We manage about 50 projects. Each project contains notes. The users creates one note each time they want to add an information on their projet.
We want to extract into a file (pdf, txt, …) the latest note of each project to have a single document containing the latest information on the projects.
Can you please explain us the easiest way to do this ?

Thanks for your answer.

There is no easy way to do this, nor hard way, except coding some report / export.

We have Template Report plugin, that can export detail on one project with all its notes, but not a list of projects with some note.

Thanks a lot for your answer.

You understand that it is quite impossible for us to click onto each project to find the information. We try to have a global action from the project list.

Is there a way to export a list of projets with all the notes ? If we can do this into a csv file, we'll be able to extract the latest note.
Or a way to export a list of projets with all the détails (containing therefore the notes) ?

No, notes are never exported on default exports.

Only way is to design your own export with notes (but CSV is probalby not the best may to represent the on-to -many relationship)