Attribute Rules (AR) is the widely promoted replacement for the Attribute Assistant (AA) tool used in ArcMap. Attribute Rules are designed for use across the ArcGIS platform, using Arcade expressions to apply calculation, constraint, and validation rules to feature classes and feature layers.
Attribute Assistant has proven to be an extremely valuable data integrity and editing tool for many Esri users throughout the years. However, AR has not achieved functional equivalency to AA as of the ArcGIS Pro 2.5 release. For example, AR does not currently have an equivalent to INTERSECTING_FEATURE from AA.
As with most things Esri, the best way to gain attention from the development team is for customers to chime in regarding the need for this functionality and how it will help/impact their business needs.
Improved AR documentation and functionality will greatly improve the user experience of ArcGIS Pro for day-to-day editing and data integrity. I am optimistic other users - especially AA users - will chime in and offer their input for improving AR in future releases of ArcGIS Pro. For those using Arcade expressions in AGOL, I am sure AR improvements will help you as well. If there are any other specific AA rules you would like to see implemented for AR, I look forward to seeing the feedback from my fellow AA users.
For the community's reference, there is currently a bug associated with this item, originally reported at the ArcGIS Pro 2.4.2 release (#BUG-000127290).