At this point in their history, the MCU is very much known for the interconnected stories that they create throughout all of their films. Each one ties into another, and many characters are given a series of films to flesh out their characters and stories in. Think the Iron Man trilogy, or the Captain America trilogy, or how Thor, Ant-Man, Doctor Strange, Spider-Man, and Captain Marvel all have another entry to their story that is set to come out in the near future. Marvel doesn't really ever do standalone films, often opting to give individual characters their own franchise-within-the-franchise. However, the upcoming Black Widow movie is going to complicate that trend a little bit.
Black Widow might have to be a standalone movie because there's really nowhere else to take the character, as her story ended when she died sacrificing herself for the Soul Stone in Avengers: Endgame. However, this might be a good move for the MCU, as it will set this story apart from its predecessors as the first character arc to really just be contained within one film and be more accessible to those who are not as familiar with the MCU.
Obviously, Natasha has had a character arc through the whole MCU, and in the films set both before and after the events of Black Widow. However, with Black Widow, she may be the first MCU hero to be able to have a solo adventure that is restricted to one film, and that might overall be a good thing. Because Black Widow is a prequel and seems to be fully earthbound, it's a great way for people who have never seen another MCU entry to engage with the franchise, and watch an independent, self-contained story that is still compelling and doesn't need to connect very much to - or set up - any other MCU entries.
In fact, one of the things that many have cited as holding back the MCU is that they always feel the need to set up future movies and characters within each movie. This was evident during the release of WandaVision, where fan theories ran rampant, and fans spent a lot of time speculating if and when cameos from other major characters would be made, or what future storylines WandaVision was setting up. Despite the fact that many of these theories proved false, the show still did quite a bit of work in the department of setting up future MCU entries, particularly things like Doctor Strange in the Multiverse of Madness, or as some have speculated, the Young Avengers.
While this kind of approach is fun for fans to engage with, it sometimes does a disservice to the story. If a film is supposed to revolve around a certain character and their story, it should be mostly about them and not be as concerned with setting up the rest of the extended universe. However, Marvel is known for its cinematic universe, and it seems it will take every opportunity possible to expand that universe in every single film.
Black Widow provides them with the unique chance to take a step back and tell a contained story. Black Widow is a prequel, so it doesn't have to set up anything in the future of the MCU. It also doesn't really have to set Natasha as a character up for anything because her arc has already ended. In this film, they can simply tell a standalone story that can focus on one character and her journey and doesn't have to connect to every future MCU entry. They can expand upon Natasha's character and give her depth without having to forge a new path for her to follow in the future. Though this doesn't seem like a novel idea for films as a whole, it's something that Marvel specifically has never really done before, and it will be interesting to see how they handle it.
It's also a good entry point for newcomers to the MCU, as it seems like it may not require a lot of prior knowledge of MCU movies. It's not a story about the other Avengers or any of the events that have happened in the MCU before the events of Black Widow, and so the story itself is self-contained. It also probably won't require much knowledge about the character of Natasha Romanoff because this seems like the film that might really get into her backstory, and so newcomers will probably be able to understand the character just as easily as long-time fans of the franchise do. At this point, Marvel isn't really trying to cater to a new audience and instead relies on fans who have already seen the previous entries in the franchise, so they don't have to re-explain events. This is a fine approach, but it will definitely be nice for casual viewers to be able to participate in the MCU without needing over 10 years' worth of superhero knowledge in their back pocket.
From the trailers, it appears to simply be a story about a former spy, her past, and how she deals with that past now, and perhaps that's all it needs to be. For once, Marvel can focus a story on a character without having to worry about connecting it to the latest cosmic threat or upcoming team-up movie. This is only the second solo film about a female character that Marvel has made, and so it would be refreshing to see it actually take the time to delve into the character and give her the development she deserves. It's been a long time coming, but hopefully Black Widow will be the most independent MCU movie we've seen so far, and be a breath of fresh air for the franchise.