It sounds like, for some reason you are not connected via ethernet. When you go into Android - settings - network does it clearly show wifi:not connected ethernet:connected?
I have run a speedtest using Ookla speedtest app on my Droix supplied machine (which is about 4 years old and also supports 5g wifi) and i am getting 250mbps d/load.
Maybe something is faulty and you should contact the supplier support? If a Droix supplied box their contact details are at the foot of this forum. Have your purchase details handy.