This particular time, the video setting have been affected. So I am trying to determine what flag has caused the video settings to be locked to 1.0.
As many of us have pointed out, this locked settings issue is
extremely normal with modern drivers, which don't play nicely with old games/api calls. In your case, Windows likely decided you needed an update and applied it, perhaps entirely in the background (i.e. no popups telling you about it). You're not having this issue because DDO recently changed something, but because they
haven't changed anything since adding DX11 support ~15 years ago.
Windows Update is constantly running. It likes to update drivers and install other stuff whenever it wants. Recently, I noticed it installed Microsoft Copilot. Before that: Bejeweled. And plenty of other stuff over the years. I never explicitly permit these installations individually, and it
never even tells me it's installing any of these things, before, during, or after the fact - it just waits for me to randomly notice them on my own. But it does this anyway, because it wants to and I agree to let Microsoft do basically whatever it wants to my machine as part of their required TOS.