How to find in array?

Simple question:

Have an array with objects (from db query):

  "query_all_subdomains": [
    {
      "school_slug": ""
    },
    {
      "school_slug": "schoolname"
    },
    {
      "school_slug": "anotherschoolname"
    }
  ]

I want to check if a value exists in the array, like: schoolname.

Thought this would be easy with formatters but I think I’m missing something.

I tried the ‘contains’ and ‘where’ formatters.

I want:

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