It is possible to enable fly mode in Creative Mode by simultaneously holding down the jump keys and opening the inventory

If you hold down the jump key while in Creative Mode and then the inventory opening key, you can enable on fly mode without even using a double jump. Reproduce:

• Make sure you're in creative mode.

• Hold down the jump key.

• Without stopping jumping, hold down the key to open the inventory.

• You will see how you are suspended in the air, but you continue to rise and fall at the same time.

• Stop holding down any key or both at once.

• Try to fly and you will succeed.