Anonymous access in Kibana is still under development, you can track progress in Elasticsearch anonymous access and Kibana · Issue #35613 · elastic/kibana · GitHub
Reverse Proxy is not an option neigter, because all I've got is a endless loading from Kibana.
Meantime, if you want to keep security enabled, you will have to use the reverse proxy in front of Kibana that sets the basic auth header. There is an example of nginx.config with the correct setup Auto-authenticating to iframe-embedded Kibana dashboard - #4 by tsullivan