The original Macintosh software also did this, back in 1984.
From the Apple Human Interface Guidelines, published in 1986:
"The application dims an item when the user can't choose it. If the user moves the pointer over a dimmed item, that item isn't highlighted."
There may well have been prior art, but that's as far back as my knowledge goes.
At least 40 years, since it was already present in Windows 1.0 (see https://www.youtube.com/watch?v=S-SuAaYDZIk for an example).
The original Macintosh software also did this, back in 1984.
From the Apple Human Interface Guidelines, published in 1986: "The application dims an item when the user can't choose it. If the user moves the pointer over a dimmed item, that item isn't highlighted."
There may well have been prior art, but that's as far back as my knowledge goes.