It's a spin-off.

Yeah right, I never realy understand what is the decision point to include spin-off into the collection. eg in the link you gave :

Other popular examples are The Fast and the Furious Collection, which includes the Tokyo Drift spin-off

It's an exception because, for better or worse, Universal count the film as part of the collection eg. Fast Five is the fifth film, including the spin-off.

From wikipédia...

Ocean's Eight (stylized onscreen as Ocean's 8) is a 2018 American heist comedy film directed by Gary Ross and written by Ross and Olivia Milch. The film is both a continuation of and a spin-off from Steven Soderbergh's Ocean's trilogy and features an ensemble cast including Sandra Bullock, Cate Blanchett, Anne Hathaway, Rihanna, Sarah Paulson and Helena Bonham Carter. The film follows a group of women led by Debbie Ocean, the sibling of Danny Ocean, who plan a sophisticated heist at the annual Met Gala at the Metropolitan Museum of Art in New York City.

After the release of Ocean's Thirteen in 2007, Soderbergh stated he had no intentions of making a fourth film, citing his desire to have the series "go out on top". However, an all-female spin-off was announced in October 2015, and much of the cast signed on by August 2016. Filming took place from October 2016 to March 2017 around Manhattan.

Ocean's 8 premiered at Alice Tully Hall on June 5, 2018, and was released by Warner Bros. Pictures in the United States on June 8, 2018, 11 years to the day after the release of Ocean's Thirteen. It grossed $297 million worldwide and received a lukewarm response from critics, who applauded the cast but found the film undemanding and less consistent than the films in Soderbergh's trilogy

It's in the ocean's world, it's a film made by cloney and Soderbergh, some caracter are in all movies... it's in the collection

Just to be sure

The film is both a continuation of and a spin-off from Steven Soderbergh's Ocean's trilogy

Thanks