Hey @steadwell – thanks for the suggestion.
Since WordPress 5.5 – the decision has been made that further tweaks to the icons in the Default Themes (like Twenty Seventeen) are no longer sustainable. You can see some more details of that decision here:
Themes field guide: WordPress 5.5
The suggested alternative for adding additional icons is using a PHP function/filter like this.
<?php
function mychildtheme_twentytwenty_svg_icons_ui( $icons ) {
$icons['calendar'] = '<svg xmlns="https://www.w3.org/2000/svg" viewBox="0 0 24 24" width="24" height="24"><path fill-rule="evenodd" d="M6.75 0a.75.75 0 01.75.75V3h9V.75a.75.75 0 011.5 0V3h2.75c.966 0 1.75.784 1.75 1.75v16a1.75 1.75 0 01-1.75 1.75H3.25a1.75 1.75 0 01-1.75-1.75v-16C1.5 3.784 2.284 3 3.25 3H6V.75A.75.75 0 016.75 0zm-3.5 4.5a.25.25 0 00-.25.25V8h18V4.75a.25.25 0 00-.25-.25H3.25zM21 9.5H3v11.25c0 .138.112.25.25.25h17.5a.25.25 0 00.25-.25V9.5z"></path></svg>';
return $icons;
}
add_filter( 'twentytwenty_svg_icons_ui', 'mychildtheme_twentytwenty_svg_icons_ui' );
That example is directly from the article I linked to, and is just example code. You’d need to adjust it so suit your exact needs for an RSS icon.