A 1.21.11 datapack that adds 2 enchantments for the ghast harness: Ghastling (III) and Joyride (III).

!Ghastling I-III

Each level of Joyride increases the Happy Ghast's flying speed and each level of Ghastling makes the ghast smaller in size (via the scale attribute).

You can also upgrade a harness in the smithing table to make it enchantable in the enchantment table directly for a greater chance of getting what you actually want

!Upgrading the harness