Visual studio is complaining that ‘UnityEngine’ cannot be found.
Tried regenerating project files.
Tried deleting all .csproj and solution files.
Tried deleting /.vs/ and /library/ folders and restarting the project.
Nothing seems to be able to make Unity understand that there is UnityEngine present in the project.
Solved the issue by uninstalling Visual Studio 2019 and installing Visual Studio 2022
Unity almost always understands. It is generally Visual Studio that loses the picture.
For future reference, this may help you with intellisense and possibly other Visual Studio integration problems:
Sometimes the fix is as simple as doing Assets → Open C# Project from Unity. Other times it requires more.
Other times it requires you also nuke the userprefs and .vsconfig and other crufty low-value high-hassle files that Visual Studio tends to slowly damage over time, then try the above trick.
Barring all that, move on to other ideas:
https://discussions.unity.com/t/778503
Also, try update the VSCode package inside of Unity: Window → Package Manager → Search for Visual Studio Code Editor → Press the Update button
Also, this: https://discussions.unity.com/t/805330/7