There is a nice tool provided by Adobe for removing bacgrounds for photos, https://express.adobe.com/tools/remove-background. I have tested it with portrait photos meant for documents, and it works very well. Can this process be reproduced with GIMP in a way this is almost exactly as automatic as on the Adobe's webpage?
after the "Foregound select" answer. I have tried the Select foreground tool. Still it seems that ccexpress does much better work. First photo shows CCexpress result (automatic) and the second shows gimp results. I have painted on the hair comb that has been included. It seems to me inclusion is too aggressive as large part of the background gets included. Or one has to be more pixel-perfect. If you think better job is possble - please tell.
With blue background both are "not ready" but CCexpress is much closed to the desired end result. In more realistic case: I want to have some light background and I shot the photo with some gray background (like a wall), I would say that CCexpress work is likely passable.