idk if this will help anyone, but I had this error on Stability Matrix on linux. The fix was to install opencv-python through the Stability Matrix interface. On the packages screen, you click the three dot menu for the package having the problem, then click python packages. From there you can install missing packages. i don't really know much about how python/conda/etc environments work on linux, because i did a whole lot of steps mentioned above and elsewhere in terminal, but it never did anything. I'm just posting this because no one has posted the fix to my problem anywhere, probably it's too obvious... anyway, just in case this might help someone down the road. Anyone that knows what they're doing, feel free to elaborate..