Honestly they have good separation of concerns in the Dutch government. And running the stack doesn't automatically mean hosting the services, there's enough local expertise in the Netherlands to run that.

A few years ago I had the mispleasure of working for the island government of Bonaire, and they kinda run the same systems as they do in the mainland, being a sort of municipality.

Since all gemeentes in the Netherlands are basically independently run but have to communicate with each other for DigiD but also the GBA (ID system) and loads of other stuff, they invented a standard. It's a SOAP based monstrosity called StUF, and you better spell it like that.

I can't find much about StUF in English, but there is this about the succesor where they lament on how engrained StUF still is.

https://www.conduction.nl/commonground/

It wouldn't surprise me that migration to common ground is what they are refering too. StUF knowledge is not widespread due to the level of vendor lock in. There's not many vendors and outside GovIT nobody cares about StUF.