@Guada Murua I think this might work.
1) Determine the role, I would suggest you probably want to create a new custom role for this purpose. As you are aiming for a read-only perhaps start with Finance or Executive User as I am pretty sure this are entirely read-only.
2) Go to edit visibility and add the new role to the list under TBM Studio
3) Consider any additional permissions that might need to be added, i.e. do you want them to be able to see Development? then you need to add "AccessDev"
4) Test it, I would suggest that you create a new login and test it using an incognito tab in Chrome or the equivalent in other browsers, I know you can use impersonate user but this can have bugs on occasion
Good luck, let me know how you go.