First a question ? Why Gimp 2.10.14 - nothing wrong with Gimp 2.10 but the last version was Gimp 2.10.38
..then of course there is now a Gimp 3.0.4 (but makes no difference to your question)
In pictures, it is all about the sequence. Using Image -> Scale Image
First change the width and height (1) I am using a percentage here, but you can see the size in pixels has changed.
I could leave it like that but I then change the resolution to half what it was (2). Why do that ? It is about print size. Go to Image -> Print Size and that keeps the original size in real world units (remember Gimp works in pixels) if you want to print it.
Now Export your 50 % scaled image (with a better scaling interpolation (3) ) and a new name to keep the original safe.
Edit: Just reading your post again 1600 ppi -> 600 ppi That is 37 % -ish I normally would not recommend going much below 50 % but up-to-you
..then of course there is now a Gimp 3.0.4 (but makes no difference to your question)
In pictures, it is all about the sequence. Using Image -> Scale Image
First change the width and height (1) I am using a percentage here, but you can see the size in pixels has changed.
I could leave it like that but I then change the resolution to half what it was (2). Why do that ? It is about print size. Go to Image -> Print Size and that keeps the original size in real world units (remember Gimp works in pixels) if you want to print it.
Now Export your 50 % scaled image (with a better scaling interpolation (3) ) and a new name to keep the original safe.
Edit: Just reading your post again 1600 ppi -> 600 ppi That is 37 % -ish I normally would not recommend going much below 50 % but up-to-you