You have not cast an artifact spell using Muldrotha this turn.
Steps
Activate Urza's Bauble by tapping and sacrificing it, causing you to look at a card in a player's hand, and then draw a card at the beginning of the next upkeep.
Cast Urza's Bauble from your graveyard by paying ({0} magic symbol) .
Displacer Kitten triggers, blinking Muldrotha.
Repeat.
Results
Infinite card draw at the beginning of the next upkeep.
Infinite draw triggers at the beginning of the next upkeep.