Does Android 8.1(Oreo) lack "Landscape Orientation" mode? I am using AospExtended v5.7 for tomato and I have noticed something weird. The rotation button in the status bar only toggles between Portrait Mode and Auto Rotate Mode. It lacks the Landscape Mode(even when I try to do it whilst holding the phone in Landscape).

Is it normal? I feel its weird because I had this functionality in LineageOS 14.1(basically Nougat), but its not in a later version.
It is normal. Even my phone has the same. I can be on either 
"Auto Rotate" or "Portrait Only".

You can reply on 3rd party apps like "Rotation Control" to force a landscape if needed.