Cannot use multiple .NET versions: v9 missing after update

Problem

After updating .NET through the package manager (APT), it is no longer possible to select version 9 of .NET when creating new solutions in JetBrains Rider, even though version 9 appears installed in the system.

Cause

The issue could be due to the .NET Command-Line Interface (CLI) path configurations or system permissions. Update processes might redirect or miss proper symlinks to the .NET executables that the Rider IDE references.

Resolution

1. Verify the installation paths of all installed .NET versions.

   • Use the dotnet --list-sdks and dotnet --list-runtimes commands to confirm installation and locations.

2. Ensure that the system/user paths prioritize the correct executables:

   • Check the configuration of PATH variables to ensure appropriate CLI path accessibility.

3. Re-integrate .NET versions in Rider:

   • Navigate to Settings / Preferences / Build, Execution, Deployment / Toolset and Build Tools.
   • Ensure that the correct .NET CLI is set for the Toolset and Build Tools path.

4. Test the setup by creating a new project to confirm all .NET versions are visible and selectable.

Additional Notes: If the problem persists, consider clearing Rider's configurations or reinstalling it to rule out possible application-side misconfigurations.