You could try the gmic Gimp plugin http://www.gmic.eu
This has an Extract Foreground (Interactive) filter. Not a lot of expertise required, just a lot of mouse clicking.
left-click for green and keep / right-click for red and delete. Various settings in the filter, try the options but a single layer updateable is a good starter.
You get a floating window to click in. Hit the space bar for updates. When finished close the window and it gets transferred back into Gimp. The background is still there if required, use the eraser tool in anti-erase (alt) mode
This example, was about 3 minutes, cut down to a minute for imgur https://i.imgur.com/aBSk3yK.mp4
This has an Extract Foreground (Interactive) filter. Not a lot of expertise required, just a lot of mouse clicking.
left-click for green and keep / right-click for red and delete. Various settings in the filter, try the options but a single layer updateable is a good starter.
You get a floating window to click in. Hit the space bar for updates. When finished close the window and it gets transferred back into Gimp. The background is still there if required, use the eraser tool in anti-erase (alt) mode
This example, was about 3 minutes, cut down to a minute for imgur https://i.imgur.com/aBSk3yK.mp4