Looking at that page, one of those empty circles is from HTML markup that looks like this:
<i class="tatsu-icon tatsu-custom-icon tatsu-custom-icon-class stroopwafel medium circle" data-animation="fadeIn" data-animation-delay="0"></i>
The CSS classes being used there are not valid for Font Awesome.
If I inspect that element in the DOM and edit the CSS classes, changing them to just “fas fa-stroopwafel,” the icon shows as expected.
That means a few things:
1. this plugin is loading Font Awesome correctly, as you’ve configured it.
2. whatever means you’re using to add icons (maybe a shortcode provided by Oshine or tatsu?) is not producing standard Font Awesome CSS classes.
It may also mean:
3. Oshine or tatsu uses its own non-standard CSS classes for icons, and may or may not be using Font Awesome.
Here’s a possible solution for you. Since we know that Font Awesome is being loaded correctly by this plugin, you could just use normal HTML <i> tags in the block editor or the shortcode provided by this plugin and avoid using any shortcodes or blocks provided by Oshine/tatsu.
If you follow the usage guidance on this plugin’s readme, it will result in standard, valid Font Awesome CSS classes, and I expect it will work as expected.
In this case, you could edit your block as HTML and just use this HTML <i> tag:
<i class="fas fa-stroopwafel"></i>