Yes, I know it is an old version, but I got Acid Pro 8 via Steam when it was on sale and Magix have never added any of the extra features I've wanted in newer versions, so I have never seen a need to update.
On to the problem. The last few Windows 11 Insider Preview builds have all broken Acid in the same way. I am unable to load existing .acd files, or save new ones. The program itself loads fine, so I don't think this is a Steam problem; no VSTs are loaded (and we know how Acid hates VSTs) so it isn't that; and every other program is fine, so it isn't Windows that is broken (any more than usual).
Before I reinstall Windows, does anyone have an idea what the problem might be? If not, has anyone experienced anything similar?