This video covers 2 different ways of capturing screenshot on OnePlus 6. The 1st method is using the default android method and the second one is using 3 finger swipe method. OnePlus 6 does provide an option to take a long screenshot as well. Hence the same is demonstrated.
The same method of taking screenshot works in OnePlus 6T, OnePlus 7 and OnePlus 7 Pro as well.