Large swathes of ArcGIS (such as Field Maps or the Experience Builder Edit Widget) now assume all attachment tables use the new schema the "Upgrade Attachments" tool generates. This means all EGDB objects that feed registered map services need upgraded attachments or various client components will fail against those otherwise functioning services. This is a massive issue for naive Pro users who enable attachments without upgrading, especially if more ArcGIS components require upgraded attachments.
All methods of enabling attachments in Pro need to create the upgraded fields by default to avoid leaving ticking time bombs in user's databases. This is also a UX enhancement as enabling attachments through the "Manage" properties tab now requires the user to jump into a GP tool for the upgrade, when it should be a single-click operation.
