Disclaimer:
I do not have 100% rock hard evidence for this (but… I think its 99.99%.), but it is certainly something that should be investigated, given that this can put anyone who uses these Assets into trouble.
I also apologize for not knowing “where to report this”, or “what to do about it”, since I dont want to accuse someone of something they might not have done without other eyes having glimpsed over it.
Lets get to the proof then, shall we?
Assetpack: UndergroundPalace in Environments - UE Marketplace
This is actually one of Genshin impacts “Sphere” Asset-Sets combined with Parts from the “Hilichurl” stuff you can find near their camps.
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Images are taken from the Trailer on the Assetpacks Store Page: UndergroundPalace(UE4 Marketplace) - YouTube
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Screenshots from Genshin Impact are mine, I left part of the UI/Character in to make it obvious which one is which.
I think that this is enough evidence, but I do have more (the fireplace, doors, the floor, other stones, etc.), I am just too lazy to put effort into this guy.
There are two more assetpacks directly copying Genshin Impact, but from what I see not ripping the assets, therefore I will not add them here.
EDIT: Its not for sale anymore, that was quick.
EDIT 2: I stopped being too lazy and dug up plenty more pieces in the game (I ignored some of the ones I already checked in the above image.):
Many more of the ones in his list I have seen in the game in the past, but couldnt find them quickly enough, but it shouldnt matter anymore, given the list of things I can clearly find.
Note: He has recolored some of the things, but it should be obvious based on the mesh on itself and the amount of things “that coincidentally are similar to the ones in Genshin Impact” 
