Under Google Search Console -> Search Traffic -> Search Analytics, I see an "Update" as in the screenshot.
Does it mean that there was an algorithm update from Google on this date?
Google is letting you know that it updated its algorithm that counts clicks on that day. If the numbers before and after the update look different, it is probably because your site was effected by the algorithmic counting change rather than a problem with you site.
If you click on the update, there is a "learn more" link that take you to this help page. Specifically for December 15th, it says they separated out website clicks and mobile app clicks. It looks like your site didn't have a drop after the update so you probably don't have a mobile app (or at least not a popular one.)
It has nothing to do with Google's search algorithm. Google releases updates to its ranking algorithms almost every day. It does not announce those in Google Search Console.