Downloads come from two places: people who search the App Store and people who see an ad. We work on both and we start with the free one, because paid installs pointed at a listing that does not convert is money set on fire.
App Store optimization is metadata work with a feedback loop: the title, the subtitle, the keyword field, the icon and the screenshots, checked against what people actually search for and what your page converts at today. The screenshots are part of the keyword work, not separate from it — most people decide on the first two frames, in the search results, before they have read a word of the description.
Apple Search Ads then runs against a break-even cost per install worked back from what a user is worth to you, rather than a budget somebody picked in a meeting. And all of it reports into cohorts, so the question of whether the last release helped or hurt has an answer instead of an opinion.