The Patriot Games ending settles the personal feud and leaves Ryan's career open, which is exactly what the sequels need. Miller kills the people who helped him and goes after Ryan alone. The two men fight on a boat, and Ryan kills Miller before the boat explodes. An FBI rescue team pulls Ryan to safety, and in the last scene Cathy's doctor says the unborn baby is healthy.
Why does Miller end up alone? In my opinion, that is the cleverest turn in the film. The splinter group that broke him out of the prison van is the same group hit in the raid on the North Africa camp, the raid Ryan follows from above through satellite images. Miller escapes that raid, then turns on his own leaders, so the story shrinks from an organization to one man with a grudge. That is a smart structural choice, because the grudge began on a London street when Ryan killed Miller's older brother, and it can only close in a fight between the two of them.
How does the finale compare with the rest of the saga? The Hunt for Red October (1990), directed by John McTiernan, kept Ryan, then played by Alec Baldwin, behind a desk and a periscope, explaining a Soviet captain's intentions. Here, in my opinion, Phillip Noyce moves Ryan from analyst to participant in four steps: the London ambush, the highway attack on his wife and daughter, the camp raid and the speedboat fight. It could be argued that the waterside house makes the stakes more intimate than any submarine standoff. The baby news is a plain way to show what he fought for, and it lands because the earlier attack put Cathy and Sally in the hospital.
There is a production angle too. Baldwin dropped out after the shooting schedule was pushed back, and Paramount signed Harrison Ford to a three picture deal that began with this film, as The Washington Post reported in 1991. The film cost $45 million and earned about $178 million worldwide, according to Box Office Mojo. Ford and Noyce then reunited for Clear and Present Danger (1994), a bigger and more political story in which Ryan is acting deputy director of intelligence and discovers a covert campaign run behind his back.
As for Ryan's CIA path, Patriot Games does not close it. He has a part time role and a family, and the film leaves the rest open. That is the thread Clear and Present Danger picks up next. The Prime Video series Tom Clancy's Jack Ryan is television and starts from a different place, so none of this ending carries into it.