Both 2017’s Spider-Man: Homecoming and last year’s Spider-Man: Far From Home, released trailers in December of 2016 and 2018, respectively.
Murphy’s Multiverse was the first to report on the Spider-Man 3 first look arriving in December.
The Spider-Man project will likely utilize a lot of CGI, so a full-length trailer may be out of the question for December since the movie just started production.
The Black Widow standalone movie was supposed to open back in May of this year, but it was not able to happen.