I just downloaded the latest v4 from the sonarr website. Installed it on a fresh windows 11 install. It insists on authentication… But what does it expect? I tried my windows credentials, no go.
So i uninstalled v4, and luckily found a v3 executable install pkg. Now back to normal.
It’s asking you to set up credentials, if that had already been done then it would be the same credentials from v3.
v4 requires authentication, but you can of course reset authentication: Sonarr FAQ | Servarr Wiki
Thanks for your quick reply.
I do not use authentication on v3 since it is running on my local machine. (In fact, I didn’t know it was an option.) There is no need. Yet, v4 insists on it to even get started… I did however look through the support wiki which offered an solution by modifying the config.ini. Set it to NONE… The seemingly worked. V4 is now running without a password for lan users(that’s me!) and a very strong password for others. 
Regards