How can I turn off the black bar on my iPad Air?

See if this support page can help you:--> View a larger version of text you’re reading or typing on iPad

After turning of Hover option, restart your iPad.

If you're talking about someting else, please better describe your issue.

Regards

Giulio

What exactly is written in the window? can you please translate it into English?

Have you tried disabling Settings>Accessibility>Hover Text?

ProustGiulio wrote:

What exactly is written in the window? can you please translate it into English?

"Please check the text or enter another one." Or something like that.