Google’s algorithm for reporting on image search impressions within the Google Search Console performance report was updated on April 6, 2021. The update that was made isn’t a result of any ranking algorithm updates, but just a reporting change, and that is it.
According to Google, the update is specific to “image impressions when type=image is specified in the Search Performance report.” The search engine did say that the result is that this could lead for you to see a “small drop” in your image search impression data within the performance reports.