title: QGIS 3 broken/disabled python
body: <p>I am encountering major Python issues with QGIS 3.  I was attempting to install 3rd party libraries from OS4GEO shell. Steps are:</p>
  <p>1- Run shell as admin; 2- py3_env; 3- pip install scikit-learn</p>
  <p>I was getting bugs there so I un-installed QGIS and re-installed it to get a clean slate of python libraries.  When I re-open the newly installed QGIS, I lose python support.  Plugin support is lost and there are no processing options. Uninstalling/Installing QGIS does not solve the problem.  Oddly enough, it is version specific. If I break 3.4, re-installing it does not fix the problem, but I can install 3.10 and 3.15 and they work.  But then if I try to add Python libraries to 3.10, it breaks and a clean install does not solve the problem.</p>
  <p>How can I reset the Python for a version, even after using the uninstaller?</p>