GIMP user: noob: forbidden layer zones -- WUWT?

Make a New File, 400x400.
Draw a little, just to prove it works.
Now, resize the canvas to 450x400.

The new 50 pixels to the right are not accessible, even after SELECT ALL. Why is that?

You can add a new transparent layer and if you want merge down this new layer.

Resizing canvas does not resize existing layers by default, there’s a dropdown in the Canvas Size dialog that lets you choose what to do with them. This is so that you don’t automatically lose size of your non-image-sized layers that you may be using for effects, text, etc… If you just want to resize whole image use Scale Image instead.

Additionally, there’s a rclick command in the Layer panel to make the layer the image size.

Uck, it’s so clumsy. Compared to Photoshop.
I guess the price is right.