Make User "Read-Only"

Is there a possibility to give a user “Read-Only” access to the dashboard. Use-case: The grandfather comes for a visit. He is interested to see values light temperature, energy, but he should not be able to change switches (perhaps unless in his room).
There is a system-user with read-only access, but how to bring someone into this group.

For me it is no solution to make the dashboard invisible. Guest should be able to look at certain values, but should not be able to change them.

Any help/ideas?