Now that I have thoroughly investigated this I can say that :
- Some Uno compatible boards that work fine on the IDE and also using CREATE on a Win10 pc are not recognised by CREATE on the chromebook
- The common element to this is that when they are recognised on Win10 in both IDE and CREATE they show as using port 4 whereas boards that work also on chromebook use port 1
- I guess that the version of CREATE on chromebook will not recognise those compatible Uno boards that work using port 4
It would be a great help if something could be done about this as it seems that quite a lot of compatible boards that I have tried (borrowed from friends) do seem to use port 4