I run a single ssid dual band network ... what tends to happen is 5Ghz is effectively ignored. 2.4Ghz has better coverage, so everything wants to live there. At least wifi 6 brought improved encoding to 2.4Ghz.
I haven't had luck with the roaming extensions; when I run them, some of my devices won't connect or won't stay connected and it's a pain to monitor. I guess I could run a different SSID with roaming enhancement, but effort.
You can turn down the power on the 2.4GHz radio so it's not as overpowering.
This used to be pretty common on at least Linux and Android clients some years ago.
Not sure if they finally got around to making the BSSID selection algorithm a bit smarter or whether all my access points just support active steering at this point, but I haven't seen this in the past couple of years.