Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
This expression, “O Allah, I do not ask You to avert the divine decree, but I ask You to be gentle and gracious with me,” should not be used in supplication, because what is prescribed for a Muslim is to ask Allah تعالى to ward off affliction and an evil decree, and to seek refuge in Him from everything that may harm him.
Imam al-Bukhari, may Allah have mercy on him, entitled a chapter: “Chapter: Seeking refuge in Allah from the descent of misery and from an evil decree.” He then mentioned the statement of the Prophet ﷺ: “Seek refuge in Allah from severe affliction, the descent of misery, and an evil decree.”
Therefore, there is nothing wrong with a Muslim asking Allah تعالى to avert affliction from him, to ward off an evil decree from him, and to be gentle with him regarding what He has decreed for him. This is because supplication itself is among the means that Allah تعالى has decreed, and supplication does not contradict belief in divine decree.
It is correct for a Muslim to say, for example: “O Allah, I ask You for well-being, and I seek refuge in You from an evil decree and from severe affliction. I ask You to avert evil and harm from me.”
And Allah تعالى knows best.