You can get it from:
- Paimon Shop, in which there are 3 methods available: Buy them for 160 Primogems each, or exchange them using 5 Masterless Starglitter each (no limit), or 75 Masterless Stardust (max. 5 every month)
- Leveling up Dragonspine’s Frostbearing Tree (you can get 2 Intertwined Fates, but only for one time)
- Paid Battle Pass/Gnostic Hymn Rewards (you can get max. 4 Intertwined Fates if you leveled up the paid Battle Pass until lv40)
- Events (some events gives you Intertwined Fates as reward)
Currently, the easiest way to get the item is by either spending Primogems, or exchanging them using Masterless Starglitter or Stardust. And according to rumors, the upcoming Inazuma region’s “Frostbearing Tree” (dubbed “Sacred Sakura Tree”) will provide lots of Intertwined Fates as its level up rewards, so there’s that.