Devices constantly changes between 2.4 and 5ghz band

I set up 2.4 and 5ghz bands on the same SSID and security. The devices constantly lost their connections to switch between 2 bands. I don't know how to config the Wifi setup that prioritizes the 5ghz band. I know some modern router of other brands has "Smart or Intelligent band steering" that allow 5ghz devices only connect 5ghz wifi band. I don't know if OpenWRT has that function. Don't ask me to blacklist MAC address of the devices to a specific band. It's very tedious to do so.

): Anyone help me please

What release are you on ?

Band steering is a quite complex thing, as clients choose which band to use and when to change the band.

See DAWN band steering.

I have not started using this, as several requirements are only available in master yet, and I run 19.07.6. .

I used Redmi AC2100 Snapshot OpenWRT

So you can try dawn, when you are on a snapshot.
The problem with the 2 different bands is, that either your client sticks to the 5ghz band, while the 2.4 ghz band is already much better, or, once the client changed to the 2.4 ghz band, it stays there forever...

Read yourself through the dawn stuff and try it out, if you need both bands and want automatic band steering.

That's the problem. I see. The algorithm is much more complicated than I thought. Most affordable router/AP has the option for two band steering and mesh function, such as Xiaomi. I tried the stock firmware and this function works perfectly. Changing to OpenWRT, I lost that function ):

I'm using Xiaomi AIoT Ac2350. Smartwifi function is already in stock firmware. How can I enable it in OpenWRT?