why is "build....desktop... directory outside of my project directory

I just discovered that the new creator is creating a file named <proj>.pro.user
and it is creating another directory named:
build-<project name>-Desktop_Qt_5_15_0_GCC_64bit-Debug.
out side of the project directory.

It is one directory above the project directory.

Could this be a problem? If I save and delete the project directory, I was
not aware of this other directory. Should it also be saved and move.
If I reuse this project folder name is there going to be any left over
problems of conflict with the previous project. (In my case is a reference
to controls/@directory.qrc which no longer existed causing make problems
because I reused a previous project definition (folder)?

I would like to see all of the project related folders be stored under the
project folder. creating separate folders does not seem a good practice
especially in terms of ISO validation terms.