I haven’t played Genshin Impact, though I have some degree of exposure via cultural osmosis, so for all I know it could have more words of lore written than Skyrim. The gacha content mill style of development certainly lends itself to that kind of quantity. Though, a quick check of the wiki isn’t encouraging, only listing 34 in-game books compared to Skyrim’s 337 (not including Skyrim’s DLC), and 568 named characters to Skyrim’s 988 (also not including DLC). But I’m willing to give the benefit of the doubt for the purposes of the rest of this discussion.
However, there’s simply no way Genshin has more lore than The Elder Scrolls series as a whole. The only other video game franchise with any hope whatsoever of matching TES for lore is the Nasuverse. All of the lore from the other games, developer roleplays, developer statements, leaked design documents, and other such sources, has its own influences on that relatively small sliver of lore that can be directly observed by experiencing Skyrim in isolation. By analogy, The Lord of the Rings may technically only have a little over 1000 pages of lore, but we all know that most of the lore that can be teased out of that text comes from the external context of The Hobbit, Silmarillion, Unfinished Tales, Tolkien’s notes and letters, and various other sources.
To put it another way, I have personally interacted with multiple people (and am aware of several more) who have done or are doing Masters or Doctorate level theses on the lore of The Elder Scrolls (just as is the case for Tolkien), and I’m anything but a notable or even particularly sociable member of the lore community, whereas I would be utterly astonished if there was enough lore in Genshin Impact to support even a single doctorate.