Then tried to install the Pimoroni Dashboard. This seemed to go well and appeared in the Accessories list. Clicking on it just gives a brief screen flash of a possible dialogue then nothing (just desktop).
As this is a new RasPi it was set up with the supplied NOOBS card which installed the latest Raspbian Buster OS.
This is an issue because buster moved to stable after this release on the SD card. If you run sudo apt update and answer yes to the prompts then re-run the curl command once the update finishes everything should be OK.
Try this, run sudo apt get update that should get you a yes no prompt. answer y and it should now update. From then on you can go back to running sudo apt-get update, upgrade
Then run the one line installer again.