An interactive ad asks for a response (a tap, a choice, a scan) rather than only being watched. That changes what is measurable: instead of estimating who saw it, you know who acted and what they picked.
The strong cases are ones where the choice is genuinely useful to the viewer. Picking a product variant, answering a question that tailors what comes next, or selecting the offer they actually want produces both a better experience and a first-party data point, which matters increasingly as third-party tracking disappears.
The caveat is that interaction rates are far lower than anyone plans for, and low is not the same as failed. A few percent engaging is normal, and the correct comparison is not "most people ignored it" but what a passive ad would have delivered from the same spend. Judging an interactive campaign by reach guarantees disappointment; judging it by the quality of what the engaged minority did is the honest measure.
Design so the ad still works for the majority who do nothing. The message has to land as a passive view, with the interaction as an upgrade rather than a prerequisite.