This package provides a custom toolbar link. Just it: a simple anchor with a name, an href, a target and a icon.
composer require nalingia/nova-simple-toolbar-link
use Nalingia\SimpleToolbarLink\SimpleToolbarLink;
//...
public function tools()
{
return [
(new SimpleToolbarLink())
->name(__('Packagist'))
->to('https://packagist.org/')
->target('_blank')
->icon('<svg class="sidebar-icon" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" width="24" height="24"><path fill="var(--sidebar-icon)" d="M8 4c0-1.1.9-2 2-2h4a2 2 0 0 1 2 2h2a2 2 0 0 1 2 2v14a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V6c0-1.1.9-2 2-2h2zm0 2H6v14h12V6h-2a2 2 0 0 1-2 2h-4a2 2 0 0 1-2-2zm2-2v2h4V4h-4z"/></svg>');
];
}