The Marvel Cinematic Universe explains how Inhuman could already be on Earth thanks to ‘Black Widow’. As the first movie in Phase 4, Black Widow's importance to the MCU's future was questioned due to its setting and Natasha Romanoff's fate in ‘Avengers: Endgame’.
The Scarlett Johansson-led film takes place during Captain America: Civil War's ending, seven years before she'd sacrifice herself on Vormir. However, the movie still introduced many characters and storylines that could play important roles in Phase 4 and beyond.
Phase 4 is rapidly expanding the MCU after ‘Avengers: Endgame’ in terms of new characters and the amount of content coming from Marvel Studios. Movies like ‘Eternals’ and ‘Shang-Chi’ introduce new corners of the shared universe, while Disney+ became the home for official MCU shows centered on established characters and some new heroes.
With Marvel still figuring out how to bring the Fantastic Four and X-Men to the universe, too, every upcoming MCU movie and TV show will in some way play a role in teasing what else is still to come. It is even possible that ‘Black Widow’ provided an explanation for how Inhumans could be on Earth already.
The Inhumans aren't usually connected to Black Widow in the comics, but Black Widow might still explain a key piece of their mythology. Inhumans are a group of Kree-created superhumans who originally live on the moon before bringing their city of Attilan to Earth as a giant floating city. It might seem as though it would be quite easy for someone to spot or find Attilan, but ‘Black Widow’ provided an explanation for why that might not the case.
The movie revealed Dreykov's ‘Red Room’ was an aerial base that constantly moved. When they questioned how no one managed to find it, the film explained that no one looked to the sky to find it. Its thin logic overall, but the same mindset could allow the MCU to reveal the Inhuman also have a floating city somewhere on Earth that no one has discovered. -Collider
