You can have a WiFi network one band only, i.e., no need to mirror 2.4 Ghz config to 5.0 GHz.
Once you set up a WiFi network and hit Save, the configs should persist. E.g., if you refresh the page after saving or navigate away from the WiFi page and come back, you should see your settings intact. If you see otherwise, please let us know. We’ll help you figure it out.