There's a ridge, kind of like a die crack along the transition line on both sides. The unplated side is slightly shallower then the plated area,which led me to chemical reaction. Wondering if it is possible to partially plate coins.
Here is an article that ends with an attempt to duplicate the mint process. Several articles seem to agree that the coating of copper is not exactly the same thickness over the whole cent, with the edges being thicker than the central areas. Also there is no reason for a reasonably straight line , and a somewhat jagged edge at that as electroplating should be somewhat diffuse in deposition. I guess if someone covered the coin with tape, glue, etc. , the covered areas would look somewhat like this. I would lean to removal based on the photo. IMO, Jim https://www.comsol.com/blogs/electroplating-u-s-mint-makes-penny/
This link shows some good comparison of genuine to fakes, which has my curiosity up about this coin. https://conecaonline.org/unplated-lincolns/