As the title says, why can't my file tree be automatically collapsed?
Preferences / Folder Tree / Options / Collapse non-selected branches
Thank you for your help, but I found that as in my picture, when I locate the directory on this computer, the directory tree has not been collapsed.
It doesn't happen when you click This PC, but it will happen as soon as you click any normal folder.
Did you mean to click "This computer" in the directory tree?
Yes. It is called "This PC" in English versions of Windows these days. A long time ago it was called "My Computer" and maybe "This Computer" at one point. Microsoft keep renaming it, to make all of our lives more difficult.
You are still clicking This PC. As I said:
It doesn't happen when you click This PC, but it will happen as soon as you click any normal folder
Click one of the drives, or a folder under one of the drives.