some ressources are Project Manager on few projects and sometimes team member on other projects

Define these resources with profile Project Member. They will be by default Project Members on projects they are affected to.
Then for projects where they are Project Leaders, just define profile for these affectations as Project Leader : yes, you can select profile for each affected project !

Ok, I tried your scenario (user test created with Project Member role and for one project, he was assigned to the project with Project Manager role) but I can't create activities with this user.

What is wrong?

Can you post some print screens for Profile definition, Affectations, Activity.

Sure, I attach the screenshots.

Let me know if you need more details.

I use v5.0.6

The default profile for the user (project memeber) cannot create activities.
Affectation as a project leader is not taken into account because project is not selected yet 😉

So, opposit to what I said first, you have to set default profile to "Project Leader'.
Keep affectation to "project member" where user is not a project leader.

Thanks Babynus

So, all Project Leader could change and create tasks on all projects. So, from security side, it is not the best (it is just my opinion :unsure: )

Do you know another solution?

When you create the role "Project Leader" and "Supervisor", what is the role with more priviledge?

all Project Leader could change and create tasks on all projects

No, Project leader can then change and create activities on projects they are affected to with a Project Leader profile.

When you create the role "Project Leader" and "Supervisor", what is the role with more priviledge?

These profiles are completely different.
Suppervisor sees all projects without have to be affected to them, but cannot change items of the projects.
Project Leader has more restricted view (only projects he is affected to) but can change almost everything on his projects.