I had a problem when copying images from Gimp (early 2.10 releases) but it was independent of image size, and turned out to be a problem with the clipboard manager (klipper for me). I temporarily fixed the problem by disabling the image support in klipper, and the problem eventually got fixed after a KDE upgrade.
Ubuntu-MATE 20.04 / GIMP 2.10.36 PPA from Panda Jim,
I created the 8bit 1x1280 > Ctr+A > Ctrl+C > works as intended, no crash.
I even tried without any layer but the canvas only, as you said to make a canvas, same > no crash (does not select as there were no layer, but no crash on Ctrl+A > Ctrl+C).
I would think like @Ofnuts , it might be something with your clipboard manager
I’ve tried the above after closing the clipboard manager, but it’s still the same.
Also four patterns I had created 6 months or so ago with 1x1280, 1x720px dimensions will crash GIMP immediately on launch as the patterns are loaded. If I remove from them from
~/.config/GIMP/2.10/patterns
then GIMP will load as normal (only to crash when copying a canvas or layer with the aforementioned dimensions).
I’ll install a totally fresh Manjaro instance on another partition and check it there.