https://9to5mac.com/2021/04/28/leaked-facebook-memo-reveals-how-advertisers-will-be-impacted-following-ios-14-5-release/
– 1-day click-through opt-out data will be modeled for advertisers.
– 7-day click-through and 1-day view-through attribution settings will no longer include iOS 14.5 opted-out events.
– 28-day click-through, 7-day view-through, 28-day view-through attribution tools will no longer be available to advertisers.
I'm not clear on what the first one does.