I downloaded the QT-Designer with 'pip install pyqt5-tools' and no error message came up. However, in the folder 'C:\ANACONDA\Lib\site-packages\pyqt5_tools' where I saved my python and the 'pyqt5-tools' object is stored I cannot find the 'designer.exe'. In all the YouTube toturials I have watched the 'designer.exe' should be found. I have installed the Python version 'Python 3.9.7' with ANACONDA.
Python 3.9.7 (default, Sep 16 2021, 16:59:28) [MSC v.1916 64 bit (AMD64)] :: Anaconda, Inc. on win32
I guess I can solve your problem since you said

'C:\ANACONDA\Lib\site-packages\pyqt5_tools' where I saved my python and the 'pyqt5-tools' object is stored

I installed pyqt5-tools via Conda environment named Python3.10. here is the path where I can find designer.exe file:
C:\Users\Shayan\Anaconda3\envs\Python3.10\Library\bin
So if you installed pyqt5-tools via a Conda environment, you can find designer.exe in a path like this:
C:\Users\<USERNAME>\Anaconda3\envs\<YOUR_ENVIRONMENT_NAME>\Library\bin
Or you can search for designer.exe via the search option of windows!
I can't find the QT Designer even though it is installed