Early reports from people who are/were familiar with the script, decribe the movie as a 1st person narrative, told from Thatcher's perspective as she suffers from dementia. Apparently, much of the story surrounds her struggling with her own "regrets" about her past life.
The Thatcher family is said to be furious, not only because of the alleged "dementia" aspect, but because all of these "regrets" told in a 1st person narrative are entirely fictionalized - in other words, they are all a fabrication born from the screenwriter's imagination.
How do you think something like that is going to turn out?
No wonder movie going is at it's lowest point in history. They have demoralized the population to near collapse. All they can sell these days is outright moral decrepitude.