What is this referring to Natural sugar or added sugar? Normally the yoghurt doesn’t have added sugars beyond what were presswnt are in the milk originally.
For sauces you can easily read the labels and find which ones contain added sugar, at least in europ it’s mandatory listing that.
Greek yoghurt (first picture) tastes fine with out added sugar but only the normal fat one 5%, if you remove fat then yes you need to add something…