You can provision a user in Looker to limit access to only viewing dashboards, using a combination of model sets, permission sets, and content access to create a role to apply to the user, or a group of users.
First, under Admin > Roles, create a new model set and select only the models containing the LookML for your dashboard(s).
Next, create a new permission set and select limited permissions. If you want users to see only dashboards defined in LookML, select:
If you’d like users to also see user-created dashboards in spaces, select the additional permissions:
To allow viewing of dashboards in spaces, you will also need to give the user access to the space in which the dashboard is saved. Under Admin > Content Access, highlight the space(s) you want to allow your user to view, and select Manage Access… Add the group or user you are creating and give them View access.
Finally, in Admin > Roles create a New Role and select the model set and permission set you just created. Select the individual user(s) you are creating, or a group of users that will be limited to dashboard-only access.