score:6
You should declare the Ukrainian citizenship because you have to complete the application truthfully. If anyone ever asks you about the discrepancy between the two applications, explain just as you have here that when you completed the first application you believed that you did not have Ukrainian citizenship, and you have since discovered that you were mistaken.
Completing the earlier application incorrectly is not a problem as long as you believed that it was correct when you submitted it.
You might want to stay away from the details of the misunderstanding, since you still seem somewhat confused. German law does not control Ukrainian citizenship. Germany could (but apparently does not) have a law requiring you to renounce Ukrainian citizenship in order to retain German citizenship, but it cannot have a law directly preventing Ukraine from granting you citizenship, nor directly depriving you of Ukrainian citizenship.
Your statement about the exemption for jus-soli Germans is therefore correct only if it somehow triggers or fails to trigger a provision in Ukrainian law that affects the citizenship of children born abroad to Ukrainian parents.