Are the mentioned adhkar authentic and helpful in memorizing the Quran, especially since they cannot be found in reliable sources?

There is no objection to the aforementioned supplication for memorizing the Qur’an, as there is nothing in its wording or meaning that is reprehensible in Islamic law. However, there is no evidence in Islamic law for specializing a specific supplication for memorizing the Qur’an, and there are no specific supplications or remembrances for that in Islamic law. The Muslim should strive to memorize and supplicate to Allah frequently to help him with it, and supplicate at times when supplication is encouraged, such as during prostration, after the last tashahhud before the salam, and at dawn.