the best async/concurrency model i know is verse [1], a language made for fortnite scripting because tim sweeney decided he wants something with "metaverse" in the name. instead of async/await or verbose callbacks its all combinators. from their docs:

  # Nested blocks for complex operations
  sync:
    block:  # Task 1 - sequential operations
        LoadTexture()
        ApplyTexture()
    block:  # Task 2 - parallel to task 1
        LoadSound()
        PlaySound()
    LoadModel()  # Task 3 - parallel to tasks 1 and 2