The accepted answer does not work in Jupyter (at least when using some libraries).
The Javascript solutions here only hide warnings that are already showing but not warnings that would be shown in the future.
To hide/unhide warnings in Jupyter and JupyterLab I wrote the following script that essentially toggles css to hide/unhide warnings.
%%javascript
(function(on) {
const e=$( "<a>Setup failed</a>" );
const ns="js_jupyter_suppress_warnings";
var cssrules=$("#"+ns);
if(!cssrules.length) cssrules = $("<style id='"+ns+"' type='text/css'>div.output_stderr { } </style>").appendTo("head");
e.click(function() {
var s='Showing';
cssrules.empty()
if(on) {
s='Hiding';
cssrules.append("div.output_stderr, div[data-mime-type*='.stderr'] { display:none; }");
}
e.text(s+' warnings (click to toggle)');
on=!on;
}).click();
$(element).append(e);
})(true);