Brave users on macOS Catalina (does not effect Mojave 10.14 and below) will initially download Widevine Content Decryption Module - Version: 4.10.1440.18.
On browser close and next restart, users will be updated to an unsigned version and will get updated to 4.10.1582.1.
Users will then get the prompt below:

Websites requiring libwidevinecdm.dylib will no longer work unless using the workaround below.
4.10.1440.184.10.1582.1Users will need to allow libwidevinecdm.dylib from Systems Preferences -> Security and Privacy -> General:

and then select open when prompted.

Close and restart the browser.
Same behavior with Widevine on websites using macOS Mojave with no additional macOS security prompts.
Easily.
Brave 70.123 macOS Catalina 10.15.1
Verification PASSED on macOS 10.15.1 x64 using the following build:
Brave | 0.70.123 Chromium: 78.0.3904.97聽(Official Build)聽(64-bit)
-- | --
Revision | 021b9028c246d820be17a10e5b393ee90f41375e-refs/branch-heads/3904@{#859}
OS | macOS Version 10.15.1 (Build 19B88)
0.70.123 enabled Widevine and checked brave://components/Widevine Content Decryption Module - Version: 4.10.1440.180.70.123 CR: 78.0.3904.97 and checked brave://components/Widevine Content Decryption Module - Version: 4.10.1582.2Once I pulled 4.10.1582.2, ensured that the netflix.com, Prime and YT worked as expected.
Kamils-MBP:~ kjozwiak$ codesign -vvv ~/Library/ApplicationSupport/BraveSoftware/Brave-Browser/WidevineCdm/4.10.1582.2/_platform_specific/mac_x64/libwidevinecdm.dylib
/Users/kjozwiak/Library/ApplicationSupport/BraveSoftware/Brave-Browser/WidevineCdm/4.10.1582.2/_platform_specific/mac_x64/libwidevinecdm.dylib: valid on disk
/Users/kjozwiak/Library/ApplicationSupport/BraveSoftware/Brave-Browser/WidevineCdm/4.10.1582.2/_platform_specific/mac_x64/libwidevinecdm.dylib: satisfies its Designated Requirement
Confirmed. Widevine Content Decryption Module - Version: 4.10.1582.2. Same set up as @kjozwiak only checked on netflix.com. Works great.
Most helpful comment
Confirmed. Widevine Content Decryption Module - Version: 4.10.1582.2. Same set up as @kjozwiak only checked on netflix.com. Works great.