How to make Raspberry pi 3b, wi-fi work at 40 Mhz?

Question

WiFi

Hello! There is a stump in Linux, so I ask for your help. So so. There is a piece of iron Raspberry pi 3b, with Raspbian Buster on board. The piece of iron is connected to a network through wi-fi. There is a MikroTik hAP mini router, in which the wi-fi mode is set to G / N / 20-40Mhz. So, the first problem was that the max. speed did not exceed 56 Mbps. She decided to remove the country from the wi-fi settings on the raspberry (up to 76 Mbps rose). Now the second problem has come out, because in RouterOS it is possible to see in what mode, at what speed and at what frequency the wi-fi client is working, I saw that devices (smartphones, laptops, etc.) operate at a frequency of 40 Mhz , while the raspberry operates at 20 Mhz. My meager knowledge did not lead my research on the Internet to anything useful. Maybe someone knows how to make this piece of iron work at 40 Mhz?