I had a jekyll blog repo at: https://github.com/truongnh1992/truongnh1992.github.io
When I share a post to facebook, it only shows the default thumbnail. I couldn’t enable the optional thumbnail.
Could you help me to figure out this issuse.
What you need is OpenGraph or OG tags. That is a standard define by Facebook for metadata
Consider using the Jekyll seo tag which will render the tags for you
Check what that head tags look like on this site built with minima theme
I don’t use the tag explicitly but you can see how a file of the theme handles it in one line
There is a tool on facebook itself for people to enter details for a link and preview how it appears.
I think this is it
This tutorial will also help
The OG homepage too