One of the folders within the datapack folder was named "overworld", after uploaded to Realms it got replaced by "over<My_Realm_Name (world 1)>" causing the datapack to not work.

Summarize: Folders that has "world" in the name gets changed into <My_Realm_Name (world_number)>

You should only make it changing the main world folder's name, not all folders. Thanks!