TOML is not a very good format IMO. It's fine for very simple config structures, but as soon as you have any level of nesting at all it becomes an unobvious mess. Worse than YAML even.

What is this even?

[[fruits]]
name = "apple"

[fruits.physical]
color = "red"
shape = "round"

[[fruits.varieties]]
name = "red delicious"

[[fruits.varieties]]
name = "granny smith"

[[fruits]]
name = "banana"

[[fruits.varieties]]
name = "plantain"

That's an example from the docs, and I have literally no idea what structure it makes. Compare to the JSON which is far more obvious:

{
  "fruits": [
    {
      "name": "apple",
      "physical": {
        "color": "red",
        "shape": "round"
      },
      "varieties": [
        { "name": "red delicious" },
        { "name": "granny smith" }
      ]
    },
    {
      "name": "banana",
      "varieties": [
        { "name": "plantain" }
      ]
    }
  ]
}

The fact that they have to explain the structure by showing you the corresponding JSON says a lot.

JSON5 is much better IMO. Unfortunately it isn't as popular and doesn't have as much ecosystem support.