Recently some users have reported incompatibility between annotation created in ArcGIS Pro 2.x and ArcGIS Pro 3.x. This document explains what is supported at the different releases of ArcGIS.
Compatibility of Annotation between ArcGIS Pro 2.x and 3.x
Those that are maintaining annotation should be aware of the incompatibility between ArcGIS Pro 2.x and ArcGIS Pro 3.x. Note that this is true for both standard and feature-linked annotation.
Annotation is a feature, stored within an annotation feature class within the Geodatabase. As with other feature classes, an annotation feature class stores the geographic location and attributes. Beginning with ArcGIS Pro 3.0, the storage of annotation has been modified to support the full cartographic model of ArcGIS Pro.
If you are maintaining an ArcGIS Enterprise 10.9.1 and have upgraded to ArcGIS Pro 3.0.x, or 3.1.x, you will be able to edit the annotation created with ArcGIS Pro 2.x. Newer properties of the ArcGIS Pro 3.x annotation are relatively minor and will be downgraded to the ArcGIS Pro 2.x version when written to the geodatabase.
Once Upgraded, you cannot go back.
Once the annotation feature class that was created in ArcGIS Pro 2.x is upgraded to ArcGIS Pro 3.x, it will no longer be compatible with Pre-3.0 version of ArcGIS Pro. Once upgraded, the annotation feature class is no longer usable in previous versions. Feature classes linked to the annotation are read-only in previous versions. Feature classes in the same feature dataset as the upgraded annotation are also read-only in previous versions.
Refer to the annotation compatibility table in the documentation to understand the different versions of annotation.
In Summary
If you have users that will continue to use, access, and edit annotation created with ArcGIS pro 2.x, you can continue to publish from ArcGIS Enterprise 10.9.1, 11.0, or 11.1 while accessing it from ArcGIS Pro 3.x. However, once the annotation is upgraded (using the Upgrade Dataset Tool), it will no longer be available for use in previous versions.