Losing Notability notes

A few ideas:

1. Restore them from a backup
2. Talk to the Notability developer to see if there are any known issues with their app and iPadOS 14.4.

For older iPads or iPads with a Lightning connector, do a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

OR

If a newer iPad Pro model, try the new hard reset procedure for the new 2018/2020 iPad Pro and iPad Air 4 models.

1. Press and Release the Volume Up button.

2. Then immediately Press and Release the Volume Down button.

3. Then, Press and Hold the Power Button at the top. You will see the Slide to Power off button, but keep on holding down the Power Button until you see the Apple logo, then let it go.

Once you have performed all the steps, wait for a few seconds and your 2018 iPad Pro will boot up completely to the iPad Pro’s Lock screen.

If still no joy,

Did you ever backup these notes to either iCloud, iTunes on a computer, Google Drive/DropBox/BOX/MS One Drive?

Notabilty gives lots of options to backup your notes in Notabilty.

You were foolish to not take advantage of all the data/notes backup possibilities.

If they are gone now, these notes are gone.

I use Notability and upgraded/updated my iPad to iPadOS 14.4 and had no issues with Notability, but I have notes/data backup everywhere, just in case something bad goes wrong with iOS/iPadOS upgrades/updates.

Always do device backups before performing any iOS device upgrades/uodates or ANY type of computer upgrades/updates.

Data backups are insurance against losing any important data permanently.

Sorry & Good Luck to You!