.dshAppContainer .embPanel__optionsMenuButton {
display: none;
}
This would be the CSS to hide it (depending on Kibana version).
If you want a quick solution you can add this into a CSS file already being used with Kibana.
For instance /kibana/src/core/server/core_app/assets/legacy_light_theme.css
if you are using the light theme (if you have dark mode set use the dark theme file). Just copy paste that into the bottom of that file and you should be good to go. Might need to clear some browser cache to force the change. (again it depends on version).
I did not check or verify that this doesn't remove the options from other pages in Kibana you might want to keep them. I think by targeting dshAppContainer
that should just hide those within the Dashboard application.
One huge side effect of this is if you upgrade Kibana that change is gone/overwritten. You will need to add it back in. That is why a custom plugin would be ideal and the best way to do this.
You could also do this change on the website where you call the iframe from but will require some Javascript because you can't apply CSS to an iframe. But you can hide elements using Javascript after the page has loaded and I think you should have that ability if you are offering an iframe. If you do the second option then that will be hidden just for the iframe users. The first option will hide for iframe and people that are logged within Kibana which you probably don't want but I am not sure on your exact use case here.