anyways since we're focusing on Hercule Poirot, let's dive into his games and see which ones are canon and which ones are not:
Murder on the Orient Express (2006) - It's an adaptation of the novel, only difference is that the novel is set in 1932 while that game is set in 1934 the year the novel was written (canon?)
Death on the Nile (2007) - Adaptation of the novel, idk if there were made some changes like in the first game (possibly canon)
Peril at End House - Adaptation of the novel, idk if there were made some changes like in the first game (possibly canon)
Evil Under the Sun - Adaptation of the novel (Kind of), it has a framing sequence where Poirot tells Hastings about this case to give him a chance to solve it, so I'd say it's canon.
Dead Man's Folly - Adaptation of the novel, idk if there were made some changes like in the first game (possibly canon)
The ABC Murders (2009) - Adaptation of the novel tho it can be played with different murderers (maybe canon?)
The ABC Murders (2016) - Adaptation of the novel, tho it has differences (maybe canon?)
The First Cases - Original story set when Poirot is in the Belgian Police, definetly canon.
The London Case - Original Story which depicts the first meeting with Hastings, a meeting only alluded to in the novels, definetly canon.
Murder on the Orient Express (2023) - Adaptation of the novel, but it's set in 2023 and features modern technology, definetly non-canon.
Death on the Nile (2025) - Adaptation of the novel, and a sequel of the previous game, oddly enough the game is set in the 1970s.... (guys, c'mon it's just 2 games, how could you break continuity so badly?) Anyways, it's definetly non-canon.
June's Journey + Agatha Christie - crossover game set in the 1920s, while the timeframe is perfect, the cases are based on Poirot Novels that are set in: 1926, 1932 and 1938 in-canon, meaning that they aren't canon with the classic Poirot timeline, so non-canon.
BONUS - games based on other novel series by Agatha Christie such as 4:50 from Paddington, Behind the Screen, And Then There Were None and The Scoop were released, but as far as I know all the Agatha Christie books does NOT share a universe.