AssetStudio-blk
Check out the original AssetStudio project for more information.
There's already another AssetStudio fork that can load Genshin Impact serialized files, but I didn't make it and therefore didn't want to distribute it without permission.
This one is a fork that I've written myself from scratch. Unlike the other fork(s), this one can load .blk files directly and properly load Texture2Ds.
See genshinblkstuff for more information about .blk decryption and extraction.