This was worded rather poorly (and harshly), but to me, actually makes a fair deal of sense.
Celebrities that have profits tied to the box office results, are going to want to maximize their return, and to that end, they will all want their movie releases delayed until the theatrical market has rebounded.
But the theatrical market can't rebound, if no one wants their movies released. If no movies get released, the theater industry eventually collapses and the potential to make back any money on a movie vanishes. Additionally with the collapse of the theater industry, hundreds if not thousands of people would be out of work.
It's going to take a long time for the market to recover to 2019 levels, and a lot of people and companies (including Disney) are going to have to suffer losses in the interim to achieve that. Johansson is basically asking to be shielded from those loses, in part because she believes that Disney could have just sat on the film until it could guarantee it would make something above $600M on it.
I think it will be extremely difficult to prove that Disney was malicious in releasing the movie this year, or even that the box office performance was significantly impacted by the Disney+ release. It can be assumed that, during a pandemic, some percentage of people viewing on Disney+ had absolutely no intention of actually going to a physical theater to see it.
If I can put on my tin foil hat for a moment, I am starting to think that she might be doing this for reasons that are not terribly obvious. I can't imagine that the amount she would be owed, if given a portion of the Disney+ numbers, is all that significant compared to the $20M she already received, and I somehow doubt that the figure she would have made, even if the movie made $600M would be all that much more either.
Maybe she really just wanted to burn her bridges with Disney and move on. Maybe she was ultimately put off by the way that Disney and Marvel both treated her character for the course of the last 10+ years. There was a lot of speculation and calls for a standalone Black Widow movie, all the way back to 2010, and it didn't materialize for a DECADE. She could have been the first stand alone female MCU lead, but instead that went to Captain Marvel, who is now lined up to make more standalone movies.
I can absolutely sympathize on that front. Black Widow was a fantastic character and Johansson played it well. She could have easily been elevated to the point of having her own line of movies, as the male heroes were given, but for whatever reason Disney/Marvel didn't see fit. She probably lost out a lot more on those previous decisions than she did on the results for Black Widow.