Touch screen problem as you can see in the picture, we can't touch the lower mid part. Do you think what is the real problem and how can we fix it? Thank you for answers.

Whether y’all think it’s a problem is up to you. I don’t get to make that call.

That looks like the display or digitizer has failed, or maybe the battery is swelling. Bad hardware.

That failure may get more interesting over time should the failure enlarge, as the screen may well become further unresponsive to touch.

The usual fix is a repair either by Apple or by an authorized repair provider.

Use Get Support in the upper right to discuss your options and alternatives with the folks that work for Apple.

Do get and do keep current and complete backups, pending repair or pending progressive failure.

Nice way to show the failure, BTW.

Presumably this is seen in that same area irrespective of what screen you're in? If so I would agree with the advice given. If it is only in Notes then a restart or reset might fix it.