I’ve been encountering this issue for some months now where I can no longer fully login to the forums when using the most current versions of Safari (on macOS or iPadOS, etc). Login to the forums still works for me with other browsers like Chrome or Edge – which is how I’m able to report this issue.
Clicking/tapping “Log In” button always brings up the new account sign up panel instead of the login panel. If I flush the browser cache for all live.com-associated pages or logout of live.com separately and then go to forums.flightsimulator.com, I’ll get the login screen and can successfully login but when I get to the flightsimulator forum page it shows the guest view again and offers the “Log In” button at the top. And clicking that button just brings up the new account sign up panel again. It’s like I’m half-logged into the forums. All other live.com associated web pages work fine and behave normally. It’s just something to do with forums.flightsimulator.com on the current versions of Safari.