IMPORTANT UPDATE
Thank you everyone for your help. You have given me expert advice especially 'Splattergames' (the FORCE is strong with this one).
I have now managed to install GrapheneOS onto my Google Pixel 8 Pro...(HOORAY).
I purchased a higher quality USB-C cable and installed Google Chrome (I then uninstalled Brave & Firefox followed by a reboot).
After I made those changes it went on easy-peasy.
thanks to you Dudes & Dudettes I am now officially a 'Brethren'.
LIVE LONG AND PROSPER...