Found a solution here: Cortana not finding Desktop apps when searching for them
Here is the relevant part:
I reinstalled Cortana using the following procedure:
Open an elevated Command Prompt window (press win + X, and then press A)
Type start powershell and press enter
Run the command (in one line):
Get-AppXPackage -Name Microsoft.Windows.Cortana | Foreach
{Add-AppxPackage -DisableDevelopmentMode -Register
"$($_.InstallLocation)\AppXManifest.xml"}
After 30 seconds the problem was solved on my machine. Incredible.
