Google makes its update from time to time. The changes made greatly impacts the search engines such as Penguin, Panda, Pigeon etc.
As per the statement released from Google on December 1 2020, they made few changes in the algorithm but nothing has been highlighted.
Many websites have seen the decrease in traffic tremendously and also the ranking for the websites has gone down.
There has been discussion in webmaster forum but nothing has come out yet.
Many users are talking about this downfall at https://www.webmasterworld.com/google/5018435.htm