I am unable to uncheck Rectangle Select's Antialiasing in GIMP, every other options works just fine, as well I can uncheck Antialiasing with every other tool. What am I missing?
The Rectangle Select tool already makes pixel-perfect selections. So, unchecking "antialiasing" would make no difference anyway.
Test it yourself and you will see. Select a rectangle and fill it with colour. Then zoom in and you will see the pixels are not anti-aliased, but solid.
Example zoomed in on rectangular selection filled black, pixel grid enabled.
The ability to switch off the anti-aliasing option only comes into play if you also enable Rounded Corners in the Rectangle Select tool options, or when using the Ellipse Select Tool, or the Free Select tool.
