Immediately Signed out of iCloud.com

I am constantly being logged out of icloud.com and sent back to the login page. This happens immediately or within 1 minute. I've used a Windows 11 Laptop (fully patched) with Chrome and Firefox browsers and also used a friends macbook with Safari to test this. In all cases, I log in and am logged out almost immediately.

I've also reset my password and Signed out of all browser sessions.

What else can I do, I am not able to get to my mail with my Windows Laptop.

Thanks for any help!