Apple is doing some cool things to make personally identifiable tracking from Facebook ads much less pervasive, while still providing advertisers/businesses data about whether or not their ads are working. These things include sending batches of data every 36-48 hours instead of data as it happens, etc. But in order for these tools to work, Apple is asking Facebook to rely on this list to see if subdomains would be able to set up conversion events to collect this anonymized batched data.
This system will make ads worse, but I think it's an alright balance. Not being able to have any conversion tracking will make ads dismal.
I wish that Apple would work to maintain their own list that served this purpose, or provided support to the volunteers that were tasked with keeping this updated.