Since due to an increase in privacy there will be no IDFA from ios 14, so to track performance there will be few changes in the camp setup of Appsflyer.
Now you need to make sure to add mandatory parameters and macro in AF tracking URL while setting up the campaign.
There will be no click id so tracking will work based on other parameter.
Tracking URL setup
Privacy Postback For Appsflyer
In your account go to Automation > Integration > Mobile Marketing platform > Appsflyer > Setup Instruction.
You can share this privacy postback with the Appsflyer and do the test as per their instruction.