Laurie Strode is a fictional character in the Halloween film franchise, portrayed by actress Jamie Lee Curtis. In the original 1978 film, Laurie is a high school student who is stalked and attacked by the masked killer Michael Myers on Halloween night. In later films, it is revealed that Michael Myers is actually Laurie’s brother.

The reveal that Michael Myers is Laurie’s brother is not made until the second film in the franchise, released in 1981. In Halloween II, it is revealed that Laurie is actually Michael’s younger sister, and that she was adopted by the Strode family after the death of her birth parents.
The revelation of this connection between Laurie and Michael was a controversial one, as it was not present in the original film and some fans felt that it cheapened the impact of the first film’s story. However, it has become a significant part of the Halloween franchise mythos and has been referenced in many subsequent films in the series.
It is important to note that the timeline of the Halloween franchise is somewhat convoluted, with multiple films ignoring or retconning previous entries in the series. As such, the question of whether Laurie Strode knows that Michael Myers is her brother can be somewhat complicated to answer depending on which films are considered canon.
In the original Halloween film, Laurie is unaware of any connection between herself and Michael Myers. She is simply a young woman who is targeted by a seemingly random killer on Halloween night. This is also true of the 2018 sequel/reboot, which disregards all previous sequels in the franchise and depicts a Laurie Strode who has spent decades preparing for a potential encounter with Michael Myers, but who is not aware of any familial connection between them.
However, in the films that do acknowledge the sibling relationship between Laurie and Michael, it is generally depicted as something that Laurie learns over time. In Halloween II, Laurie initially has no knowledge of her connection to Michael, but begins to experience flashbacks and nightmares that suggest she may have some sort of link to the killer. It is eventually revealed to her by Dr. Loomis, the psychiatrist who has been tracking Michael for years.
In subsequent films in the franchise, it is generally assumed that Laurie is aware of her connection to Michael, although the details of how she learned this can vary. For example, in Halloween H20: 20 Years Later, which takes place after the events of Halloween II but ignores the subsequent sequels, Laurie is depicted as having faked her own death and assumed a new identity in order to escape from Michael. Her teenage son, played by Josh Hartnett, is aware of his family’s connection to Michael and is tasked with helping his mother face her fears and confront her brother.
In the most recent film in the franchise, Halloween Kills (2021), Laurie’s knowledge of her connection to Michael is not directly addressed. The film picks up immediately after the events of the 2018 film and focuses on the aftermath of Michael’s killing spree in Haddonfield, Illinois. While Laurie is shown to be recovering from her injuries sustained in the previous film, the question of whether she knows that Michael is her brother is not a major plot point.
In conclusion, whether or not Laurie Strode knows that Michael Myers is her brother depends on which films in the Halloween franchise are considered canon. In the original film and the 2018 sequel, there is no indication that Laurie is aware of any familial connection between herself and Michael. However, in the films that do acknowledge the sibling relationship, it is generally depicted as something that Laurie learns over time, either through flashbacks, nightmares, or the revelations of other characters.