I would like to know if it is possible, when adding a member to the project, to allow it to see only some folders and files in the project?
the underlaying Git repository does not account for different view permissions. I’d suggest splitting the current repository/project into multiple repositories, and use Git submodules for example. Think of frontend, backend, docs and manage the access permissions in the separate projects. The global project which includes the sub modules has the CI/CD builds, sensitive data, etc. and has limited access.