Whilst not doubting your report, I can only suggest that you carefully re-read the linked information - as the gestures are reliable.
If you continue to have difficulties, try a forced-restart of your iPad - as doing so will often resolve an isolated software glitch:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
If this still does not resolve your issue, you should seek assistance directly from Apple Support - using either the Get Support link at top-right of this page, or the excellent Apple Support App:
https://apps.apple.com/gb/app/apple-support/id1130498044