The (not - configured) structure has id "minecraft:endcity" and the struture in the end lists as "minecraft:end_city".

It is now imprtant as worldgen is now publicly accessible via datapacks, not an internal concept

Since all identifiers use snake case consistently, suggesting encoding structure name as 'end_city', the same way you have fixed all instance of 'village_snovy'

Attached screenshots of vanilla world gen json for end_city structure

There are another related issues that point to different identifiers related with end cities:
MC-187911