Top Posts & Pages icon / image is not showing

The images appear to be displayed properly on my end:
https://i.wpne.ws/gQd7

Did you manage to solve the issue by yourself?

Thanks Jeremy,

The issue is not with post thumbnail but with icon / image in not showing on the left side of ” Top Post”, like it is showing (in green colour) on left side with ” Search on this website”.

I see. That icon is managed by your theme. It seems your theme adds specific icons before specific widgets, but I assume the theme author only added support for the core widgets, not for other widgets added by third-party plugins.

Luckily, you can use CSS to add your own icon, like so:

.widget_top-posts h3:before {
    content: '\f07c';
}

You can add that CSS to your theme stylesheet, or to your custom CSS editor available under Appearance > Edit CSS in your dashboard.

In the example above, I used the same icon as the one appearing before the Categories widget, but you can of course use other icons. You can find a list of all the icons you can use, and their code, here:
https://fontawesome.io/cheatsheet/

Thanks Jeremy for all your help. It worked like a charm.

Have a wonderful day!