I've seen this ship floating around my feeds for years, and honestly, it's one of those things that warms my heart and makes me chuckle at the same time. In the community around 'Genshin Impact' people absolutely pair Aether with Xiao in fanart, fanfiction, and roleplay—it's a popular ship because Aether is a blank-slate protagonist who can be written as gentle, curious, or steady, while Xiao is this stoic, tragic guardian who slowly lets people in. The contrast is dramatic and emotionally satisfying, which is catnip for writers and artists.
That said, canon? Not really. The game itself hasn't established any romantic relationship between them. Most of the material that supports the ship comes from player interpretation: quest interactions, certain voice lines, and the emotional beats in Xiao's story. I love browsing ship tags on Tumblr and Pixiv, and what fascinates me is how different creators read a quiet look or a saved life as something romantic. If you're into it, there’s a ton to enjoy, but be ready to keep it headcanon-level unless miHoYo ever writes them together officially.