@Forhadul
Sorry that the router function or feature doesn't meet your requirements. The Archer AX20 doesn't support Bandwidth Control, it only supports QoS.
We don't know much about the hardware and firmware limitations, so we will not know if it will support bandwidth control in the future, but we have feedback to the related department already, they will consider this seriously, and the bandwidth control feature may be available on the wireless routers in the future firmware update. You are suggested to pay attention to the official website, or the new firmware notifications on your router web GUI for any new firmware updates.
If this functionality has determined the choice of equipment, you can return the router to the place of purchase as not as described. If you do need this feature, you need to find one that already supports it.