My USB-C port also works when connecting the tablet to a PC so it’s definitely not just for charging. Unfortunately I cannot test it with OTG storage as I don’t have an adapter. Sorry.
@TWICE: Just checking. Are you sure your adapter is plugged in properly? I don’t know how long it is but it seems like it sticks out quite a bit. The USB-C port on my tablet was initially very tight and when I plugged in the charging cable for the first few times I didn’t push it far enough.