Following miHoYo's tradition, each x.2 version release marks the conclusion of the initial phase of the Archon Quest, introducing a new deity. Patch 4.2 is no exception, as Furina is confirmed to have her own banner in this version. Alongside the new deity comes a new weekly boss, and you encountered it in the current 4.1 version.
The next content may lightly spoil the storyline of the 4.1 patch Archon Quest

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Specifically, the new weekly boss is the colossal whale appearing in Chapter 4 of Furina's Archon Quest series. According to leakers, this boss is named 'Ptahur The Devourer' and could be the 'original' version of the whale summon that Childe uses in his weekly boss encounter. However, the specific connection between Ptahur, Childe, and Fontaine remains unknown. It's highly likely that we'll have to wait until the 4.2 patch is released.
In the game's storyline, Childe once descended into the Abyss and encountered Skirk, a mysterious young woman (?) with extraordinary swordsmanship. Skirk mentored Childe, granting him the ability to transform into the 'Demon King Costume' and the skill 'Dark Arts: Leviathan Devour' (essentially summoning a whale to crush opponents). It's highly likely that we'll learn more details about how Childe survived in the Abyss and even his meeting with Skirk.