I've just installed Ubuntu 24.04 on my 2017 iMac. Purchased Cider and tried installing Cider 2.6.1 with deb package and flatpak. Selecting "Sign in with Apple ID" doesn't do anything on either. Updated to 2.6.1.1 on both installs and I get the Apple sign in and that seems to succeed, but get the authentication error. I can log into Apple Music website just fine.