If you choose to tap zero artifacts as the second chapter ability resolves, the reflexive triggered ability still triggers, but deals no damage to the target creature or planeswalker.

You don't choose the target creature or planeswalker as you put the second chapter ability of Yotia Declares War on the stack. First, you tap any number of artifacts. Then, a second "reflexive" ability triggers (denoted by the phrase "when you do") that requires a target. Players may respond to the reflexive triggered ability as normal, and they will know how many artifacts were tapped when they do.

As a Saga with read ahead enters the battlefield, its controller chooses a number from one to that Saga's greatest chapter number. The Saga enters the battlefield with the chosen number of lore counters. Neither choosing the number nor putting the counters on the Saga use the stack, and neither can be responded to.

Yotia Declares War was mistakenly printed with the word "artifact" omitted from its final chapter ability, and it has received an update to its Oracle text.