I got Calibre portable maybe 5 or more years ago.
Because I wanted different libraries for different collections like Comics, Fiction books, non-fiction books, etc, I had created different libraries. For some reason Calibre refused to create these inside the Calibre Library folder in the Portable folder. It created them in the root folder as shown in the screenshot below. However, it worked just fine with this structure.
I used to back up the entire parent folder on an external and copy it onto any laptop I wanted (for example for my nieces who are avid readers) and it always worked just fine.
Also, every time Calibre prompts me I update the portable version to the latest version so it is the very latest right now as well.
I cannot do a System Restore as it is a brand new laptop and it will delete all the official programs that my office has painstakingly installed.