Oh you mean make it sticky. Gotcha.
You should be able to create an HTML widget to do that and even add in something in "Display Condition" to have it expire automatically.
The basic HTML part would look like this (if you're using full friendly URLs) - using this thread as an example:
HTML:
<p>
<a href="https://xenforo.com/community/threads/fix-thread-in-widget.179529"><img source="https://xenforo.com/community/attachments/annotazione-2020-04-23-105152-jpg.223173/"><br />XF 2.1 - fix thread in widget | XenForo community</a>
</p>