In the 10.14 version, I created a new directory /c/ with the root account, and then built two subdirectories /c/qtproject /c/shareproject, all of the documentation are placed in these two subdirectories.
After updating to 10.15, the entire directory /c/ is gone!
You should look in the "relocated items" folder that the installer makes.
You can find a handy article about this here:
https://www.macrumors.com/guide/relocated-items/
That folder tree was probably moved to "/Users/Shared/Relocated Items" as part of the migration process. A "Relocated Items" folder alias to that location should have been created on your Desktop during migration. A PDF in that folder explaining the contents resides inside that folder along with items that were relocated. The recloated items folder exists in part to the changes which came with macOS 10.15 Catalina with the introduction of a read-only root volume for the OS.There is a process you can use to restore that directory tree to the 10.15 root folder by creating a symbolic link in root directory using the synthetic command (see man synthetic.conf). For a better explaination and how to see Creating root-level directories and symbolic links on macOS Catalina