Bug report: https://fogbugz.unity3d.com/default.asp?1365496_3glhf07k25hpr8vn Issue tracker: https://issuetracker.unity3d.com/is...erates-csproj-with-the-wrong-language-version Unity VS package generates csproj files with <LangVersion>latest</LangVersion> which is the wrong C# version for Unity. Because of this bug, Visual Studio and VS Resharper plugin are suggesting C# 9 code improvements which are not supported by Unity yet. My tool versions: Unity 2021.1.15 Unity VS package 2.0.11 Visual Studio 2019 [16.11.31624] (This is selected as External Script Editor in Unity preferences) Repro steps: 1. Open the attached project in Unity and see that there is only one script called Script1. 2. Go to External Tools section in Unity preferences window and click "Regenerate project files" button. 3. Open project root folder in computer's file browser app. 4. Right click on "Assembly-CSharp.csproj" file and open it in a text editor (Avoid using VS for this to be able to isolate the bug). 5. See <LangVersion>8.0</LangVersion> entry in the text editor which is the correct C# version for Unity. 6. Close the text editor. 7. Right click on Assets folder in Unity project window, create a new script and name it as "Script2". 8. Wait for Unity to recompile (Even for an empty project, it takes very long bug that's another problem). 9. Open "Assembly-CSharp.csproj" file in text editor again. 10. See <LangVersion>latest</LangVersion> entry which is the wrong C# version for Unity. This problem happens randomly but very frequently. If you don't see the wrong C# version in step 10, repeat the process starting from step 7 and use a different script name everytime like Script3, Script4... The bug is going to occur eventually. For me it happens for Script2 or Script3 very frequently. 11. Go to External Tools section in Unity preferences window and click "Regenerate project files" button again. 12. Open "Assembly-CSharp.csproj" file in text editor again. 13. See that this button fixes the C# version: <LangVersion>8.0</LangVersion> 14. You can continue this loop starting from step 7 again.