everything other than Allah through His causal efficacy becoming complete in time.

If this is impossible, then either nothing comes into being—which contradicts what we observe—or events come into being without a cause that itself comes into being, which invalidates the argument. Thus, the argument is invalid under every assumption.

Alternatively, you may say:

If an infinite regress in effects is possible, such that He brings one thing into being after another without being a fully efficacious cause from eternity, it follows that everything other than Allah comes into being, and the argument is invalid. If such a regress is impossible, it likewise follows that events must come into being from the eternally fully efficacious cause. All events must therefore come into being from Him, and this entails that the world comes into being, invalidating the argument for its eternity. Thus, the argument is invalid on either assumption.

This matter has been discussed at length elsewhere.

[Revisiting ‘Abd al-‘Azīz al-Kinānī’s Commentary]

As for ‘Abd al-‘Azīz’s statement:

“It has thus been established that there are here a will, one who wills, and something willed; speech, a speaker, and one spoken to; power, one who possesses power, and something subject to that power. All of this precedes creation.”

This may be understood in two ways.

The first is that by “something willed” he meant what is conceived in Allah’s knowledge as the object of His will; by “something subject to that power,” what is established in Allah’s knowledge; and by “one spoken to,” the recipient established in Allah’s knowledge who is addressed by the command that brings into being, as Allah Most High says:

“His command is only, when He wills