The soring order applies to online ordering items automatically, however on POS, it needs to be enabled.
This section describes how to enable defined sorting order on point of sale (POS).
Twirll Login > Admin > Manage Locations > Select Location > Advance Settings > Select POS Sales Channel
Goto Manage Location Section and select the desired location
Goto Advance setting to edit sales channel wise settings.
Select the POS Settings and scroll down to Item settings.
Sorting Order to be enabled to reflect the defined sorting order of item in settings.