We have recently updated and released our new Shopify Product Taxonomy API, and what you are seeing is the new format of the GID’s, specifically the ProductTaxonomyNode has been replaced with the TaxonomyCategory type.
The links that @AcidPi has shared above are correct and up to date with our new Taxonomy API resources:
This is our new Taxonomy Explorer and will show you the updated Taxonomy Categories, Breadcrumbs, and Attributes, along with a mapping to the old ProductTaxonomyNode IDs on the right.
This is the new github repo with the updated taxonomy resources you can use for integration with your apps, and the following can also be used to map the old TaxonomyNode IDs with the new TaxonomyCategory IDs
Here’s also some relevant Shopify.dev documentation for references to the new Taxonomy API objects and queries, and a Shopify.dev Changelog post for the Taxonomy update as well.