I just noticed that you are using MacOS Catalina. I am still using Mojave and just went through the process outlined in that link to start watching netflix. (I have been using safari for all video streaming until now.) I know Catalina has not been the most elegant upgrade for Mac (buggy) so I have yet to upgrade. I will review the issue further.
I manually deleted to all Brave files in the Application Suuport folder in my ~/Library … I found 2 Application Support and ApplicationSupport (don’t know why there are 2 of these) and then disabled the spctl using the command sudo spctl --master-disable and then re-installed Brave. After opening Netflix, I got the DRM extension alert and then I went to the chrome://components and then updated the Widevine component. Now I can watch the video files. after this I enabled the security again sudo spctl --master-enable