How to convert nested Json to csv in python?

Question

I've seen some similar questions but all those answers did not work for me unforunately.

I have a structure like this:

[
{"device": {
          "key1": "value",
          "list_key": [
                   {
                    "key1": "value",
                    "key2": "value",
                    "key3": "value",
                    "key4": "value",
                    }
                    {
                    "key1": "value",
                    "key2": "value",
                    "key3": "value",
                    "key4": "value",
                    }
                  ],
          "key2": "value",
          "key3": "value",
          }
},
{"device": {
          "key1": "value",
          "list_key": [
                   {
                    "key1": "value",
                    "key2": "value",
                    "key3": "value",
                    "key4": "value",
                    }
                  ],
          "key2": "value",
          "key3": "value",
          }
},

]

I want to create a csv out of this. I have the following issues:

1. The Json is nested
2. the list_key can contain multiple nested jsons, it can be 0 but 6 as well, we dont know.

What is the best approach? I tried to use pandas json_normalize() but that did not really gave me the right format

Also I used this flattening function;

def flatten_json(y):
    out = {}

    def flatten(x, name=''):
        if type(x) is dict:
            for a in x:
                flatten(x[a], name + a + '_')
        elif type(x) is list:
            i = 0
            for a in x:
                flatten(a, name + str(i) + '_')
                i += 1
        else:
            out[name[:-1]] = x

    flatten(y)
    return out

Expected output: Each line 1 device like this:

key1,listkey.key11_0,listkey.key12_0,listkey.key13_0,listkey.key14_0,listkey.key11_1,listkey.key12_1,listkey.key13_1,listkey.key14_1, key2, key3