AIX files created in ArcGIS Pro do not open in Adobe Illustrator, or text appears incorrectly.
An update was provided for Adobe Illustrator, and Esri provided a fix for BUG-000145439.
There is a discussion of this issue in the Adobe Community forums: Unable to open .aix file in Illustrator. In this discussion, there is a link to a recommended setting change in Adobe Illustrator which resolves this issue.
In one scenario, a user reported receiving an "update available" message when running Illustrator CC 26.3.1. The issue was resolved after after applying the update and downloading and installing a new version of Illustrator, then downloading the updating the ArcGIS Maps for Adobe Creative Cloud extension.