@joaopfcruz Unfortunately the current version of the OpenSearch Dashboards allows for a read-only mode with Dashboards only enabled.
This can be achieved by defining a role in the below option in opensearch_dashbnoards.yml and assigning it to the individual users.
opensearch_security.readonly_mode.roles: ["read_only"]
Please also be aware that read-only mode in OpenSearch Dashboards doesn’t mean that the user has read-only access to the data and other OpenSearch Dashboards objects.
Your read-only user should also contain a kibana_read_only role for OpenSearch Dashboards objects and any read-only roles suggested by @jasonrojas to prevent write access to indices.