Can we still use deferred deep linking in ads?

This will depend on support from each ad network. If supported by the ad network, similar to the functionality we offer for GDPR compliance, Branch will be able to reference link data for deferred deep link behavior without performing ad 'tracking'. We believe this is fully compliant with Apple's ATT policy, since this policy deals specifically with tracking, attribution, and audience creation (core app UX functionality like deep linking is not in scope).

To put it another way, deep linking and deferred deep linking from ads is allowed regardless of ATT opt-in, so long as no tracking is performed.

That being said, certain networks like Facebook have stated that they will not support deferred deep linking for SKAN campaigns. This is likely for technical reasons, as they've decided to rely exclusively on SKAdNetwork for attribution and have no mechanism in place to pass through the deep link data for any purpose.