How do I update my site thumbnail/preview image?

When posting a link to my site in social media such as facebook and Twitter, and in SMS text messages, the preview image shown is for the template used to create the site, instead of the actual site.

This topic has been asked before, but the answer is out of date and incorrect.
How do I update my site thumbnail? - Publishing help / Editor - Forum | Webflow

Please update.

Note: the instructions on this official page only applies to the thumbnails shown on the Dashboard in Webflow, not the images provided to outsiders.

Here is my site Read-Only: LINK
(how to share your site Read-Only link)