[2020] Cannot use my ability?

Sounds like an input issue - start by restarting Steam and Vermintide 2, and verify your installation if unsuccessful:

1. Right-click Vermintide 2 in your Steam library sidebar
2. Select ‘Properties’
3. Select the ‘Local Files’ tab
4. Select the ‘Verify the Integrity of Game Files’ button. This may take several minutes

If the issue persists, look in to what other programs are running on your PC - SteelSeries Engine, for example, is notorious for producing input issues.