I have Norton 360 deluxe running on Windows 11 Pro v25H2 OS build 26200.8737
In the Norton desktop app (see upload below), if I click on Account settings (but it can be any of them, not only that one), I get a HTTP Status 400 – Bad Request (see second upload). I have reinstalled Norton and rebooted multiple times.
If you are using a VPN or ad blocker extension in your browser try turning those off and test. I just tried Account Settings and was connected to my Norton Account.