Hi @craigus111
Welcome to the Sonos Community!
The only way you can “force” the speakers onto 5Ghz would be to separate the 2.4GHz and 5GHz bands so their SSIDs (broadcasted network names) are different, and only letting Sonos know the credentials for 5GHz. I’m not sure if this is possible on Google Nest devices.
If, however, the bands are combined, then the speakers and router should be negotiating which band they should be on - 2.4GHz if the range is high and 5GHz if the 5GHz signal is strong enough (5GHz has a lower range) - this is called Band Steering and may be needed to be enabled in the Nest settings.
There’s more info here: https://support.google.com/googlenest/answer/6293481
For advice specific to your Sonos system and network, I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.
I hope this helps.
"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein