But can Green Lantern make Kryptonite with his Ring? Or would it be like if he tried to make spinach, it would look like it but not have the flavor or anything.
Furthermore, rings can be used to create energy blasts of various types. The construct creation ability wouldn’t allow a Lantern to create functional kryptonite, but one could use the energy projection function to emit kryptonite radiation, which has been done in the comics before.