@Dimson 

Hello, thanks for asking.

Theoretically, the Deco will select the best channel automatically to have good Wi-Fi performance and it is unable to change the Wi-Fi channel or channel width on the Deco manually. 

If you notice that your Deco Wi-Fi network is sharing a channel with several other networks, don’t worry. Crowded isn’t the same as busy, even though some channel scanning apps tell you one specific channel is bust, they don’t always measure other sources of congestion and interference. Non-Wi-Fi signals (like those from microwaves, Bluetooth devices, cordless phones, garage door openers, baby monitors, etc.) can all congest a channel but may not show up in a scan. So it’s possible that a channel can appear empty, while it is, in fact, saturated with other kinds of interference.

If your Deco Wi-Fi network is using a crowded channel but you aren’t experiencing slow speeds, don't worry. Your point is always scanning its environment to choose the channel that is most likely to give you the best Wi-Fi.

BTW, you may try to enable the 2.4G only for the guest network and enable 5G for the main to give it a go, then monitor the performance, which may be a good try.

Hopefully, that answers your question but let us know if you need more details.