命名空間：

using System.Text.Json.Nodes;

讀取JSON：

// 讀取設置文件參數
JsonNode json = JsonNode.Parse(File.ReadAllText(Environment.CurrentDirectory.Replace("\\bin\\Debug", "") + "\\settings.json"))["appSettings"];// 畫布參數設置
JsonNode canvas = json["canvas"];
this.qrWidth.Text = canvas["width"].GetValue<int>().ToString();
this.qrHeight.Text = canvas["height"].GetValue<int>().ToString();

settings.json 文件內容：

{"appSettings": {"authorizationCode": {"server": "","code": "13014596002","msgTitle": "請先授權","msgContent": "請先輸入授權碼，點擊驗證按鈕！","failureTitle": "授權失敗","failureContent": "授權失敗，校驗未通過，請重驗證！","success": "校驗成功"},"canvas": {"width": 300,"height": 244}}
}