Who is the best stakeholder to collaborate with if a Product Manager wants to discuss...

An Enabler Feature is a type of feature that supports the development and delivery of future business features by extending the architectural runway, improving the infrastructure, or addressing compliance. An Enabler Feature is usually defined and prioritized by System/Solution Architects, who are responsible for designing and guiding the technical aspects of the solution. Therefore, the best stakeholder to collaborate with if a Product Manager wants to discuss an Enabler Feature for the upcoming PI is the System/Solution Architect, as they can provide the necessary technical expertise, guidance, and alignment.

References:

Enablers - Scaled Agile Framework

System and Solution Architect/Engineering - Scaled Agile Framework

PI Planning - Scaled Agile Framework