Is it usually bad ad targeting or confusing onboarding that kill app activation?

Ran a quick test campaign on android and get cheap installs but almost nobody actually started using the app after signing up.

Hard to tell if the ad just brought in curious clickers who don't really care about tracking workouts, or if my first screen has way too many buttons and steps.

For anyone who faced this early on, how do you figure out which side is actually broken first?