Unity solution not compatible with visual studio

I was having similar issues when doing a clean download of an existing Unity project onto a fresh install of Visual Studio Community 2019.

In the end the issue for me was that, although the correct version of VS Tools for Unity was installed, it was 'Disabled' by default in VS's Manage Extensions dialog (Extensions -> Manage Extensions). Just had to click 'Enable', restart Visual Studio, and all worked as expected again.

Please try following steps:

• Delete old *.csproj and *.sln files on project's root folder
• Check "Edit > Preferences > External Tools" and make sure you've selected "Visual Studio"
• Re-open solution by "Assets > Open C# Project" menu

Turns out it was an issue with my existing install of Visual Studio Tools for Unity (VSTU).

I found a thread where users had experienced similar problems due to an unsupported version of VSTU running on Unity5.2 and beyond. Unity 5.2+ requires VSTU 2.1 or later for VS to work correctly with Unity, more information for anyone interested is available in the documentation here.

I had VSTU 2.3 installed, but removing and reinstalling VSTU resolved the issue, so there must have been a problem with my install. If anyone else has this or a similar issue you can download the latest installer for VSTU here. Thanks to all who chimed in your responses helped me look in the right place!

For me it was enough to right click the solution in Solution Explorer and run "Resolve errors".