Yes, it is in CMYK mode! @Stephen Marsh
By @Nicholas5DE5
Then you have your correct answer! :]
The Camera Raw Filter expects RGB input, not CMYK.
If you have a grayscale mode file, Photoshop can automatically handle the 1 channel > 3 channels > 1 channel processing behind the scenes.
You'll also notice that Bitmap, Indexed Color and Lab mode are also unsupported. Surprisingly, Multichannel mode is supported, but it's only for the active channel which is treated as grayscale.