If you're exploring that dynamic, Ao3 is basically the undisputed central hub. That archive hosts the vast majority of what gets written, and the tag system is essential for navigating. You can get very specific with tags like 'Xiao/Venti (Genshin Impact)', 'Modern AU', 'Angst with a Happy Ending' – it lets you filter out exactly what you don't want. I tend to avoid Wattpad for this pairing; the search feels messier, and a lot of the content skews younger, which isn't really my taste.
For something a bit more niche, checking Chinese fan platforms like Lofter can be rewarding if you're okay with machine translation or reading raw. The tone and tropes there sometimes differ from Western fanfic norms, which is interesting. It's not my first stop, but when I've exhausted Ao3's top kudos'd fics, I'll take a look. Honestly, most of my reading time is spent scrolling through Ao3 tags and muting the ones I'm tired of.