When you first added that building, it only had the tags landuse=residential and residential=apartments. It didn’t have a building tag, so it makes sense that it wasn’t rendered as a building. Now that you’ve added the building tag, it does.
building=apartments renders just fine, as do virtually all values of building=* (kocio would know which values, if any, are intentionally not rendered). If the iD preset is adding building=apartments, then I don’t see an issue.
I’d used iD’s suggestion to tag it ‘Apartment complex’, which gives the tags first identified:
landuse=residential
residential=apartments
I didn’t realise the presets also offer ‘Apartment building’, which is what you’re saying renders properly:
building=apartments
(Sorry, I know that’s the tag I referred to in the original post: thinking there was just one preset, I assumed iD had put that tag in since it’s the right tag in the wiki for ‘apartments’)
This tagging is not made to be used for each single building, but for the area on which the buildings are standing (here the buildings are used for apartments).
You couldn’t see anything new on the map after adding landuse=residential here for the first time, because there is a larger landuse=residential (relation https://www.openstreetmap.org/relation/9110471 ) in this town, which is drawn with the same colour as your input on the OSM Standard Map.
I think iD is right, but there can be a misunderstanding if you see: a) the area on which there are apartments or b) the apartment buildings themself. Here the iD developpers thought at case a).