App.Config values is not returning correct, null values is displayed

While using this statement - "ConfigurationManager.AppSettings[<key>]" in the project, it returns a null value even though values are defined properly.

For refernce --->

Microsoft Visual Studio Community 2022
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VisualStudio.17.Release/17.1.0+32210.238
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Visual C++ 2022 00482-90000-00000-AA726
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ASP.NET and Web Tools 2019 17.1.358.51495
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Azure Stream Analytics Tools for Visual Studio 2.6.5000.0
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C# Tools 4.1.0-5.22109.6+0c82c4114a4e4b8b723b915eee3b13261db6717f
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Office Developer Tools for Visual Studio 17.0.32009.00
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Razor (ASP.NET Core) 17.0.0.2206201+62a2c1d6162f828801565a7ca26d9d48b810a05b
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SQL Server Data Tools 17.0.62201.12090
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