EUDIW is part of the eIDAS 2.0 regulation of the European Commission. The regulation lays out several rules and regulation on how wallets should be used and how member states should deploy them. Also several rules lay out the mandatory requirement for member states to make certain data (specfifcally the PID) available for their citizens, and to accept wallets from other countries. Even though all these regulations are high level and typically non technical, the impact of the regulations is very much impactful on the technical layer, as it mandates pan European interoperability and scalable, multi party trust, as wall as significant scalability.
The eIDAS regulation delegates the technical and architectuaral layer to the eIDAS technical working group, who have created the Architecture Refrence Framework (ARF) as the technical guidance on how to implement the ecosystem from a techncial and trust perspective.
The ARF lays out a number of open and less open standards, all with their own governance bodies:
IETF PAR (RFC9126)
IETF DPoP (RFC9449)
The above set contains several standards that are not 'mature', and often also not tested at scale or across multiple sectors.