An elegant way to flatten objects in anonymous json

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Hi.
C# Issue a head:
I have an anonymous Json.
I need to disassemble only the internal objects (those surrounded by curly braces) and flatten them.
This should be done in a generic way so that no matter what the depth of the object (a child can contain an infinity of children and grandchildren) - all objects that are in curly brackets (and only they) will be flattened out into the Dictionary.
Please look at the following example:

{
  "A": "xxxxx",
  "Groups": [
    "xxxxx",
    "xxxxx",
    "xxxxx"
  ],
  "B": "xxxxx",
  "C": "xxxxx",
  "D": "xxxxx",
  "E": "xxxxx",
  "F": "xxxxx",
  "G": null,
  "H": "xxxxx",
  "I": {
    "H": "xxxxx"
  },
  "J": {
    "K": "xxxxx",
    "L": "xxxxx",
    "M": "xxxxx",
    "N": "xxxxx",
    "O": {
      "P": "xxxxx",
      "Q": "xxxxx",
      "R": "xxxxx",
      "T": "xxxxx",
      "U": {
        "V": "xxxxx"
      }
    },
    "W": "xxxxx"
  },
  "X": {
    "Y": "xxxxx",
    "Z": "xxxxx"
  },
  "AA": {
    "AB": "xxxxx",
    "AC": "xxxxx"
  },
  "AD": {
    "AE": "xxxxx",
    "AF": "xxxxx"
  }
}

I need the result to be:

"H": "xxxxx"
"K": "xxxxx",
"L": "xxxxx",
"M": "xxxxx",
"N": "xxxxx",
"P": "xxxxx",
"Q": "xxxxx",
"R": "xxxxx",
"T": "xxxxx",
"V": "xxxxx"
"W": "xxxxx"
"Y": "xxxxx",
"Z": "xxxxx"
"AB": "xxxxx",
"AC": "xxxxx"
"AE": "xxxxx",
"AF": "xxxxx"

Please note also the second object in Json ('Groups'): it should not be part of the flattened list.

What I have tried:

I tried using SelectTokens like this:

var allLevels = schemaObject.SelectTokens("$..*").Where(t => !t.HasValues).ToDictionary(t => t.Path, t => t.ToString());

but it also breaks down the most external parameters (for example: "A") and the "Groups" into three objects (when in fact I do not want it at all).