is there a rotoscoping tool
Trying to do something like this in this video, where I can just
select an object and cut round it but with just one image and not a
video.
https://youtu.be/bwudLlEi11Q
is it possible please?
A quick look at the video and it seems that roto-scope is a method of extracting a defined area from a background.
All sorts of ways in Gimp. Do a search for extract foreground. There is such a tool in Gimp. I did this little video (duration two and a bit minutes) as a demo for someone who could not get their head around it.
https://youtu.be/d3QP4isEfi8
It is not my favourite. There is a good interactive foreground extract in the gmic gimp plugin www.gmic.eu Depending on the image, scissors tool to make a selection or create a path around the subject and path-to-selection.