The old 'popup' login box has been removed. I also noticed that the in sub logins where they used to have username/password entry boxes have been removed.
More reddit enshitification to try and make us use their horrible UI.
Not that I remotely want to defend reddit, but from a development standpoint it's much easier to maintain and secure a single login workflow. Whatever nonsense the new/old font ends require, it's probably much easier to make that work with a single unified token than it is to maintain both separately.
As long as the login remembers which frontend it came from, I wouldn't be too up in arms here. If it dumps you out to www/new.reddit then that's completely fucked and there's no excuse.
I clicked your first link and it worked for me. It seemed to remember my having logged into Reddit at some point in the past. Although now that I've visited Reddit today, I feel dirty:-P.