I've never seen an error like this and don't know where to start. I installed opencv with

conda install opencv

and am running Ubuntu Linux 18.04 using a conda environment named fpn. How should I even approach debugging this?

Traceback (most recent call last):File "test.py", line 5, in <module>import cv2
ImportError: /home/s/miniconda3/envs/fpn/lib/python3.7/site-packages/../../././libgnutls.so.30: symbol mpn_add_1 version HOGWEED_4 not defined in file libhogweed.so.4 with link time reference

There seems to be a problem with the recent releases of opencv packages for Conda. I have tested all the 4.x releases and found that the problem occurs starting from 4.3. Unless you really depend on >=4.3, forcing a version prior to 4.3 solves the problem,

name: test
channels:- anaconda- conda-forge
dependencies:- python>=3.8- opencv<4.3

in my cases this installed 4.2.0. Importing cv2 in Python works fine then. Note that using conda update didn't work for me and I still got the error, but I had to first remove the environment and then re-create it. I think this behavior indicates that the error is rooted in some dependency of opencv, which is not properly down-graded when conda update is used.