What I think happened after the film's ending
At the end of the movie, Miles is revealed for the murders of both Andi and Duke.
After Miles learned of the napkin's existence from Lionel, he killed Andi to prevent her from revealing it to the public. Immediately after the murder, he was seen leaving the house by Duke, who deduced Miles's involvement with Andi's death once news of it was released on the internet during the party. Duke attempted to blackmail Miles, prompting Miles to poison Duke with pineapple juice, which Duke was allergic to, before using Duke's pistol to shoot Helen. Helen locates the napkin in Miles's office and reveals her true identity to the group. However, Miles burns the napkin and smugly brags there is no evidence against him. With the group unwilling to side with her, Helen destroys Miles's glass sculptures before triggering the Klear-powered mansion to explode. This destroys the Glass Onion and the Mona Lisa, which Miles had had on loan from the Louvre. With Miles's reputation ruined due to the painting's destruction and Klear being proven as dangerous, the group decides they will testify against him. Helen and Blanc sit on the beach as they watch the police arrive.
Miles would be taken to court and the group including Helen, Claire and Lionel testify against him with Claire being forced to get involved with Klear. Miles would then lose millions (maybe billions) to Helen in the case and Helen would open up a fund in honor of her sister's memory, and the group would continue their respective careers while supporting Whisky after the loss of Duke.