If you do not see any installs and events from Apple Search Ads in your AppsFlyer Account it means that you have not set up the tracking.
Remember, that SearchAdsHQ receives the information from the MMPs. This way if there is no information to pass we can't receive it.
So always make sure you have set up AppsFlyer to receive installs and events before integrating it with SearchAdsHQ.
Here's how to set it up in AppsFlyer https://support.appsflyer.com/hc/en-us/articles/213747963-Apple-Search-Ads-Configuration#Setup.