Use a Text Replacement Shortcut

- After copying ϟ, go to Settings > General > Keyboard > Text Replacement.

- Tap the + icon to add a new shortcut.

- Paste ϟ into the Phrase field and type something easy like :sats or :koppa into the Shortcut field.

- Now, whenever you type :sats (or whatever shortcut you set), it will auto-replace with ϟ.