The next Phase 4 movie may be very close to beginning production, as Black Widow could begin filming as early as late February.
This report comes from Omega Underground who has learned that production could begin as early as February 28th, with locations in Croatia and Miami being used. There’s no official synopsis for the movie yet, and the one that sites have been running was proven to be fake and pulled from an old non-Marvel version of the movie that was in development at one point.
The movie is supposed to be a prequel of sorts, and rumors say it could be set in the late 90s with the Y2K panic as a backdrop for the story. There’s no release date set, and there probably won’t be until Marvel officially announces the Phase 4 movies at SDCC in July, but Black Widow is expected to take the May 1, 2020 release date Marvel has staked out.