Linear endings are found in much of genre fiction. The plot is a jagged series of events leading up to the big finish. Suspense is built, there are some diversions but the build up continues. un til two opposing forces collide and one side triumphs. Anything written beyond this is anti-climax
With linera strategy, the writer must keep narrowing the parameters of the story. Subplots and diversions must be brought to an end before the climatic ending.
When the ending happens, the story ends. There is no after thought Trying to tie off forgotten loose ends during the climatic scene muddies the ending and lessens the impact. The moment the central question is answered, this is the end. Don't go into explanations. This may be why I dislike those tacked on afterwords showing the hero and heroine getting married, having a baby six months later. Some readers don't like to see the story end with that final kiss and the I love you. They want it spelled out and for other readers this makes the story fall flat.
Things not to do"
Add a new setting with paragraphs of new description. If you can't fit any descriptions into the action, you should bring it in before that climatic ending.
Add new characters and stop to let the reader know about them. This is going to dull the impact of the explosion you're aiming for.
Don't add a new plot. All this will do is bother the reader. When the story has been told it's over. Save the new plot for the next book.