I'm unable to find any of the hats in any chests in my modpack. I've attached the list of mods I have. I am using the default config file and we've looted a lot of different kinds of chests. There hasn't been hats in any of them.

modlist.zip

I am using 1.16.5 and have tried a few world gens and even in creative to see and I have yet to find a hat. I played the all of fabric modpack as well and was able to find hats easily, so I'm not sure what's causing the hats not to spawn.

I figured out the issue. The hats only spawn in vanilla Dungeons. All of Fabric used repurposed structures to add a lot more dungeons in the game, making them easier to find.

Once I found a vanilla dungeon (the cobblestone room with monster spawner and 1-2 chests), I found a hat.