Добавьте файлы проекта.

ChursinBorovik.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0-windows</TargetFramework>
+    <UseWPF>true</UseWPF>
+  </PropertyGroup>
+
+</Project>

ChursinBorovik.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.31729.503
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ChursinBorovik", "ChursinBorovik.csproj", "{596DD8C8-C4FD-49C5-A0D4-B7BAD0523B29}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{596DD8C8-C4FD-49C5-A0D4-B7BAD0523B29}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{596DD8C8-C4FD-49C5-A0D4-B7BAD0523B29}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{596DD8C8-C4FD-49C5-A0D4-B7BAD0523B29}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{596DD8C8-C4FD-49C5-A0D4-B7BAD0523B29}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {8E495C32-8F88-43D9-9C04-3D9DBAB45946}
+	EndGlobalSection
+EndGlobal

Class1.cs

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+ using System;
+
+namespace ChursinBorovik
+{
+    public class Class1
+    {
+    }
+}