I have been using the Brave browser for a while. But several days ago I observed that I was not able to use Prime Video (the videos from Amazon). Prime Video would ask for an update for the Widevinecdm extension. Following the recommended steps did not work. I did this:
First, install the chromium-widevine package (from AUR).
Second, rename the old file:
mv ~/.config/BraveSoftware/Brave-Browser/WidevineCdm/libwidevinecdm.so ~/.config/BraveSoftware/Brave-Browser/WidevineCdm/libwidevinecdm-old.so
Then create a symbolic link:
ln -s /usr/lib/chromium/libwidevinecdm.so ~/.config/BraveSoftware/Brave-Browser/WidevineCdm/libwidevinecdm.so
After this, Prime Video and Netflix work in Brave.