Radio silence from he tp-link folks on this, I have the same issue.  My home Internet is wifi from my provider that uses the 2.4 ghz for the bridge backhaul.  That signal is as loud as they come and my deco M5 APs still use that channel and basically wreck my providers connection to me basically making my Internet useless.  So clealry what every they have looking for busy channels isn't working.  If I could change those 2.4 channels or turn one or 2 of the APs 2.4 ghz off that would fix the issue.  This thread is over a year old so thinking not really a priority even those it says it has been sent to R&D multiple times.   I guess returning them maybe the only way to resolve the problem...

So basically TP-LINK don't seem to give a crap about their customers. This is the very disappointing. Its a very basic feature and the fact that they even lied saying last year that they would solve the issue makes it even worse. 

@Hami Still can't set wifi channel. Just wondering if we have any updates on being able to set this function. The channel interference is causing my hulu app to drop connection in the middle of a show.  Hulu says its the ISP. ISP says its my equipment. 

@Chipower I think tp link just cares in selling new stuff they don't care about old ones. They promisse custom channels they promess they guest network working in ap mode still not here I pay for a piece of crap in theory is good but in real life is pure crap. Tp link please just hear your costumers. 

This is unbelievable. A year later and we can't change the Wifi channel? This is one of the most basic features that exists. I hate to do it but I need to return the Deco I guess. Just way too limited.

@Kevin_Z 

In light of the Covid-19 situation where the entire world is attempting to work/learn/interact via the internet, TP-Link has an opportunity to earn some goodwill by quickly correcting this limitation.  I've got about 10 networks stacked on the same channel as my Decos.  When I connect via ethernet to my modem, I'm getting speeds of 150Mb+.  Last check on the Deco was 74k.  In other words, my wife and I can't work, and my kids are unable to do their online schoolwork. TP-Link has a real opportunity to build goodwill among a struggling customer base, by quickly (within days) adding this requested functionality.  Or we will all likely jump ship.  Feel free to pass this honest feedback up the chain.

@SpencerT just install a set of 2 M4s purchased today, seems that I got robbed as cannot change the busy WiFi channel used. Any plans to fix it or should I give it back?

I'm seeing my 5GHz channel 40 as the only channel used by my Deco M9+ setup. A network scan shows more than 40 wiffi networks using this channel in my neighbourhood. One other network is on channel 44 with every channel wide open. 

Given the increase in folks working from home, as noted in an above comment, I see performance degrading. 

It looks like this has been an issue, and a promise for sometime. @Tplik When will you have something for us? 

I must admit the solution works well for the most part, but issues like this (not being able to change the channel) and the backhaul network and QoS issues (resolved in the most recent firmware upgrade) it surpises me how basic the configuration capabilities are.