Not only its built in, but syntax is on another level, i.e. you don't need to learn special syntax if you know PowerShell. This thing alone makes pwsh worth it instead of using number of other tools.

    @{ Hello = 'world'; array = 1..10; object = @{ date = Get-Date } } | ConvertTo-Json
 
    {
      "array": [
        1,
        2,
        3,
        4,
        5,
        6,
        7,
        8,
        9,
        10
      ],
      "object": {
        "date": "2024-07-03T21:07:21.6562053+02:00"
      },
      "Hello": "world"
    }

Powershell has the upper hand here!

Still, bash can try to keep up using json.bash. :)

    $ source json.bash
    $ declare -A greeting=([Hello]=World)
    $ json ...@greeting:{}
    {"Hello":"World"}

... is splatting the greeting associative array entries into the object created by the json call.

Without the ... the greeting would be a nested object. Probably more clear with multiple entries:

    $ declare -A greeting=([Hello]=World [How]="are you?")
    $ json @greeting:{}   
    {"greeting":{"Hello":"World","How":"are you?"}}

Vs:

    $ json ...@greeting:{}                                
    {"Hello":"World","How":"are you?"}