ImportError: cannot import name 'InvalidSchemeCombination' from 'pip._internal.exceptions'

Solution
Manually remove or delete the pip file and pip-20.2.4-py3.7.egg-info file from the directory, which in your case is located in /Users/user/opt/anaconda3/lib/python3.7/site-packages and for some it's in /home/sawan/anaconda3/lib/python3.7/site-packages.
2.Now use conda remove --force pip to completely remove pip from your system.

finally use conda install -c anaconda pip to install pip in your anaconda environment.