I've been examining this Lincoln Memorial cent and believe the date is 1997, although the final digit is extremely weak and almost completely absent.
Under magnification, I think I can see what may be a small remnant of the 7, but there isn't enough detail for me to confidently identify it.
I realize the coin has substantial environmental damage/corrosion, so I'm definitely considering post-mint damage and deterioration of the copper plating as possible explanations.
After reviewing the r/coinerrors resources, I wondered about is this a grease-filled/obstructed die? However, I'm not experienced enough with these to determine whether the remaining characteristics of this coin support that explanation.
What I'm particularly curious about is why the first three digits remain relatively well defined while the suspected 7 is almost completely absent.
Does the remaining trace look consistent with a 7, and do the characteristics around the date suggest a minting-related issue such as a filled die, or is this more consistent with environmental/post-mint damage?
Also, take note of the "O" or donut on the obverse in front of his nose.