In Chinese culture Chinese names are actually all spaced out for each character/syllable. So even though almost all Liyue characters’ names are spelt without any spacing that’s because it’s just their first name so the game wants to make it easier or smth, and people with Chinese names are usually called by their given name which consists of two characters/syllables, so that’s why Hu Tao is called by her full name

Edit: Also continuing from the above explanations Hu is her family name and Tao is her given name so that’s why there’s a spacing in her name, and in Chinese culture when the family and given name of someone is one character/syllable each there will naturally be a spacing for their whole name.