@zing Thanks for the link, unfortunately the issue was that they had not set the WiFI region code.
The default setting for the recalbox.conf Wifi region is JP which would explain the issue with the high channels not being seen. I have previously updated the Wifi Region section of the recalbox.conf to be GB & US, but its still not able to connect to the 5Ghz Wifi higher than channel 48
As a further test I created another SD card with RetroPie on and was able to go straight in and change the Wifi region then in the scanned networks I was able to see my 5Ghz network (currently on channel 108)
Also in Rpi OS lite - it can detect my 5Gz network before I have gone into raspi-conf to change the Wifi region.
It just seems the is an issue with recalbox in seeing 5Ghz networks on channels higher than 48
Is there anywhere else I need to update the configuration or the Wifi region?