Google has documented that on October 28, 2020 it has, in some cases, misclassified some Google Discover data as video in the Performance report after it has been fixed. This may result in “a drop in your Discover report’s video appearance statistics,” Google said.

Google wrote:

So this seems to only impact those who get Google Discover data.

Another important note is that this does not impact your Google Discover traffic in any way, it was just a reporting issue and had zero impact on you showing up in Google Discover.

Forum discussion at Twitter.