Have you tried to use any other flags and had issues as well? For example if you use open -n -a /Applications/Brave\ Browser.app/Contents/MacOS/Brave\ Browser -n --args --incognito are you able to launch an incognito window?
Also, since it sounds like your concern is CORS specific (which I’m guessing you’re disabling to test a website you’re building) do you encounter the CORS errors if you use an extension as well for disabling CORS such as Moesif origin & CORS Changer?