@Chris64
You do not say which tool you are using so guessing that you are using the scale tool for the resize. Gimp has the option to view the contents of an image outside the canvas size. See what you have View -> Show All More of those dotted line boundry markings red dotted this time for the canvas. If that is ok then Image -> Fit canvas to Layers does what it says.
Always another way: Image -> Scale Image scales the whole thing, canvas / layers /...
examples: https://i.imgur.com/qHxUs8P.mp4
You do not say which tool you are using so guessing that you are using the scale tool for the resize. Gimp has the option to view the contents of an image outside the canvas size. See what you have View -> Show All More of those dotted line boundry markings red dotted this time for the canvas. If that is ok then Image -> Fit canvas to Layers does what it says.
Always another way: Image -> Scale Image scales the whole thing, canvas / layers /...
examples: https://i.imgur.com/qHxUs8P.mp4