The bounce rate reflects the percentage of people who clicked on a Post (or visited one of your web pages) & then closed the content within 10 seconds or what Google Analytics calls, single-page visitors.
Why is this? It could be related to a number of issues.
Neil Patel describes in this article how to decrease the bounce rate.
If you are sharing 3rd party articles you need to consider whether the content of the article is interesting to your audience. The title or text that you used to share your Post interested them enough to open the Post but...when they arrived they were disappointed & left the Post.
With so much information available online today do some A/B testing on the same topic & test your Posts to see what has the least bounce rate.
You need to connect with your audience via your Post so that they are engaged & curious enough to convert & click on your Widget.