Since iOS 13, Apple has introduced prioritization to AASA loading/resolution. Only these two classes of domains are prioritized:

  • com, .net and .org
  • the user’s ccTLDs.
(mentioned in WWDC19 as a one-liner on a slide; starting from 10:00)

To my knowledge, Apple hasn’t defined the intended effect of or any SLO for (de)prioritization in any their public domain documentation.

In practice, this means users are more likely to encounter universal link “failure” (where AASA is not prioritized to be loaded) on more exotic/niche TLDs like .io or .link .

Coincidentally, many linking platforms provide subdomains with these niche TLDs as their out-of-the-box setup.