The router mostly fails (real world) do band steering.. in the end it's the client that picks the band.
The function called band steering on some later routers was introduced for this purpose plus a host of new IEEE standards.. but it mostly works badly or not at all.
Let me clarify what you mean.
Could you give an example?
Also confused at what one wifi network means.
Can the router discriminate the 2.4ghz WiFi or the 5ghz WiFi and have only one WiFi network to
connect via?
Are there newer dual band routers that can do the radio discrimination while having one wifi
network ?
A router that is dual band cannot produce one wifi network. It must have two or three in case of TRIBAND.
So what you mean is one SSID?? ie just one wifi network name.. but it is always two actual networks.
If you check what band steering does perhaps that can support what you want. NOTE.. it mostly does NOT work.
Smallnetbuilder has loads of tests of routers and for most that offer band steering will attempt to test how well it works.
However band steering is mostly used for roaming. For a device that is parked in one place and not moved it will seldom have issues with which band to use.
This is the start of a 4 part article that covers band steering on mesh products.
https://www.smallnetbuilder.com/wireless/wireless-features/33195-wi-fi-roaming-secrets-revealed
In this case the router will choose the band .. 2.4ghz or 5ghz that a client should use.
The summary at the very top of the article.. covers most people's real world experience.
Wi-Fi marketeers continue to promise "seamless" roaming and frustrated Wi-Fi users continue to believe them, especially when vendors promise their products use special techniques to bend Wi-Fi devices to their will.
In the end it is the device that picks the band.