Dell U2413 and MacBook Pro Late 2013 Sharpness

Hey Community,

I have purchased a MacBook Pro Late 2013 13inch.

I already own a Dell Monitor U2413.

The MacBook has the newest firmware and all other updates installed.

The Monitor lacks sharpness. The text is not as sharp as it is on my Retina Display and not as sharp as it has been before, when I used a Windows Laptop by HP.

For connection I use a DisplayPort cable.

I hope you can help me.