Strange status bar icon on Samsung devices after using Developer Options I have a Samsung Galaxy S8 phone running Android 8.

I have enabled Developer Options today and after I finished with it, I disabled it again. 

The problem is that a strange icon has left on the status bar. This icon appeared immediately after I enabled Developer Options.

Here is a screen of it. 

What's this icon and how can I hide it?

Thank you very much for your help.
The icon appears to be for when the device is locked to "Portrait" mode. Or in simpler terms, when screen rotation is turned off.
It is most likely inbuilt into the phone and was there before. In case it wasn't, you can disable it from the SystemUI tuner.
Simply tap and hold on the gear (settings) icon which you see when the notifications bar is pulled down. That will enable the SystemUI tuner. In there, select status bar and disable the icon for Auto-rotate screen.