things ive found interesting in the genshin impact files:

Genshin runs on the Unity game engine, version 2017.4.30.0 (UnityPlayer.dll)

Audio files are in “encrypted” md5 format (Audio_(language)_pkg_version)

No C#_Assembly.dll file. Considering that miHoyo includes the fact that you cannot use third party mods on their terms of use, its pretty clear why its not there. (C#_Assembly is used to create Unity game mods.)

Models and other assets are stored in blk files.