Two histories complicate any simple account of Chukwu, and both concern how his prominence came about.
The first is the oracle. At Arochukwu, in the southeast of the Igbo country, stood an oracle known as Ibini Ukpabi, which the Aro traders operated and which drew petitioners from across the region to submit disputes for judgement. The Aro built a commercial network on the reputation of that oracle, and the name Arochukwu carries Chukwu in it. Some historians have argued that the Aro association did a great deal to raise a somewhat distant high god into the prominence he later held, projecting a local oracle's authority onto the supreme being across a wide area. The British destroyed the oracle in the Aro expedition of 1901 to 1902, having concluded that it underwrote the slave trade.
The second is translation. Christian missions reached the Igbo country from the 1840s, and the translators had to choose an Igbo word for God. They chose Chukwu, and Chineke alongside it. The choice was reasonable and it was also consequential: from that point every Igbo Bible, hymn, sermon and catechism reinforced an identification of Chukwu with the God of Christianity, and the vocabulary of the older religion was read back through it by everyone, including its own adherents. Scholars who describe Igbo religion as monotheistic are sometimes describing a religion that mission translation had already reshaped by the time it was written down.
Neither history means that Chukwu was invented recently. It means that the shape of his prominence has a history, and that a reader should hold the standard account, of one supreme being served through intermediaries, alongside the knowledge of how that account came to be written.