Is there a way of docking the extension toolbars to the workspace as they seem to float around when the page is minimised or moved to access another window?
Your profile says you are on Mac. Alas, this is one of the things the Mac SketchUp GUI does not handle well. We’ve complained about this for a long time, but no change.
Hi. Thanks for that “good” news 
Well, if on Windows how would I fix this issue please?
On Windows you can dock extensions toolbars to any of the four margins of the modeling client area. If you find difficulty docked them, make sure that “Show Window contents while dragging” is switched on (check the box.)
See:
Enable or Disable Show window contents while dragging in Windows 11 | Windows 11 Forum