Hi @Matelot and sorry for the hassle with this.
Here are two options that may help:
You could use a prototype view link and share it with your colleagues/clients. The only downside to this option is that they won't be able to add comments.
You could set the project’s access control slider to Blog, as detailed here. This way, anonymous users will only be able to view and comment on a project.
On a side note, this will be way easier in the next major release that we are preparing for our web product.
Hope this helps in the meantime!