I have a Jetson AGX with JetPack 4.5. I have uninstalled openCV 4.1.1. I have installed Python 3.8 by building it from source. Then I installed opencv 4.2.0 from source built with CMake. I see opencv 4.2.0 is installed in site-packages for Python 2.7 and 3.6.9. But not for Python 3.8. I have spent an entire day trying to figure out how to get opencv installed for Python 3.8 and nothing has worked. Python 3.8 has been installed in alternate location /use/local/lib.
That didn’t really solve but I did some digging in OpenCV’s root CMakeList.txt and was able to set a few additional attributes which resolved my problem. It still created a sub-folder for the install path as python3.6. However, it used python3.8 interpreter for building.