@IanAlmighty 

You can set the 6GHz SSID to the same as your 2.4/5GHz SSID after configuring your 6GHz WiFi to "Wi-Fi Network & Backhaul".

I haven't tested it myself as I don't have any 6e-compatible devices. I'd be interested to hear if the 6GHz devices can then see the 2.4/5GHz devices, and vice versa.

  @cocofyn I don't think it is related to not being able to see those bands from a 6GHz connected device.

I don't use Spotify any more but Apple Music on my Android phone sees Google Nest speakers (not Amazon speakers) but is unable to cast to them when the phone is connected on either the 5Hgz or 6Ghz.

Mind you I'm not using my XE75 at the moment so not sure this comment is useful.

  @cocofyn 

Thanks for this - I can't believe I'm so silly and didn't try renaming the SSID!

I renamed it and yes my phone is on the 6GHz with the same SSID as the 2.4 and 5GHz devices. Finally yes it does appear that my 6GHz phone can communicate with 2.4+5GHz bands... i.e. I can use Spotify although I have disabled isolation 

  @IanAlmighty 

That's good to hear.