Hello :)
(I am modding with curse forge, playing version 1.20.1 using fabric)
So, I'm aware that other people have had this issue and I was reading through closed posts to see if someone had already posted something explaining what to do and I came across: #426

and it seems they had solved so I attempted to replicate what they did by pasting the animals in the animal mod that I was using (naturalist, (i didn't add the mod name Infront of the animals if that affects it))
I loaded into my game just fine, but it didn't seem to do anything.
I have been able to turn into all the mobs I've killed so far including modded ones I just can't seem to fly.

I've gone into the identity file to check and fly is set to enabled and it's not locked behind an achievement.

I am posting this on my phone so I can't send the game log now but will if I need to.
Does anyone know what I need to do solve this or any useful videos that could help?
Thank you.

Hi
I had the same problem, I changed my flying.json like this and it works now.

{
  "replace": true,
  "values": [
    "minecraft:ghast",
    "minecraft:bat",
    "minecraft:blaze",
    "minecraft:parrot",
    "minecraft:phantom",
    "minecraft:bee",
    "minecraft:ender_dragon",
    "minecraft:wither",
    "minecraft:vex",
    "minecraft:allay",
    "naturalist:bluejay",
    "naturalist:butterfly",
    "naturalist:canary",
    "naturalist:cardinal",
    "naturalist:dragonfly",
    "naturalist:finch",
    "naturalist:firefly",
    "naturalist:sparrow",
    "naturalist:vulture"
  ]
}

Hope it works for you too :)