Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
It is necessary to distinguish between the Pen with which Allah wrote the decrees of creation and the pens that people manufacture and use for writing.
The Pen of Divine Decree is a real, created pen. Allah, Exalted is He, created it and used it to write the decrees of everything. We do not know the reality of its nature or how it is. The Prophet ﷺ said: “Indeed, the first thing Allah created was the Pen. He said to it: ‘Write.’ It said: ‘My Lord, what shall I write?’ He said: ‘Write the decree, what has been and what will be until eternity.’”
As for the pen used by people for writing, there is no harm in saying that it is an invention and product of human beings. This does not conflict with the fact that the Pen of Divine Decree was among the first things Allah created, because they are two different things.
Nevertheless, the pens manufactured by human beings—and indeed all their actions and industries—are included within the creation of Allah, Exalted is He. He is the Creator of His servants, the Creator of their deeds, and the Creator of everything in the universe. The servant is genuinely an actor and maker of what he does, and there is no contradiction between these two matters.
In conclusion: The Pen of Divine Decree is a great created pen with which Allah wrote the decrees, whereas ordinary writing pens are products of human craftsmanship. There is no contradiction between the two statements.
And Allah knows best.