Only app groups on Home Screen are available all others vanished

Try a forced-restart of your iPad - as this will often clear any post-update issues:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If the issue remains after the restart, you may need to reset your Home Screen layout:

Settings > General > Transfer or Reset iPad > Reset > Reset Home Screen Layout