This feature only works if you are using Template 1 or Template 4.
Sometimes if you have more FAQs, you might want to make categories collapsible which would allow you to hide all FAQs below it. This would make your FAQ page shorter in height.
Step 1: Visit app > Design & settings > Display Settings > Enable 'Make categories collapsible' > Save.
Step 2: Verify your FAQ page by visiting dedicated FAQ page.
If you wish to hide top bar categories on template 4, you can disable those by turning off following setting:
Navigate to app > design & settings > scroll down to "Premium Template Additional Configuration" at bottom of settings page > check "Hide categories that appear at top of FAQs"