Choose Applications ▸ KeePassXC.
Choose Tools ▸ Password Generator.
Switch to the Passphrase tab.
A very strong passphrase of 7 random words is automatically generated.
It is impossible to recover your passphrase if you forget it!
To help you remember your passphrase, you can write it on a piece of paper, store it in your wallet for a few days, and destroy it once you know it well.