I have a problem with smart connect function. The router covers mostly 2 rooms and only 4 devices  - 2 mobiles and 2 laptops. But with smart connect function it mostly switch to 2.4 Ghz band. Even if the device has fastest connection via 5GHz or is in front of the router and doesn't switch automatically on 5GHhz which I need for example for 4k video. With this simple test was streaming better via 5GHz. By the speedtest.net I have in 2.4 GHz speed about 60Mbit/s but with 5GHz I  measured about 150Mbit/s. I must point out that this happens even if there is only one laptop on the network connected.
So,  how can I prioritize 5GHz band with preservation smart connect function? Is the only way to split network to 2.4 and 5GHz with  2 different SSID? Or throw into the trash?

Thanks in advance