I do not think the procedure as described is valid with Gimp 2.10 Default layer modes.
However, on the basis that the idea is to highlight blemishes so that the base color layer is improved using the heal tool, this is the closest I can get using Gimp 2.10 default layer modes. It is the (red + green = yellow) layer in Linear burn which makes the difference. Dodge is still dodge, although you can tweak the grey colour . White is HSL color mode.
The whole thing is a bit flaky. Best bet use the legacy modes while they still exist.
However, on the basis that the idea is to highlight blemishes so that the base color layer is improved using the heal tool, this is the closest I can get using Gimp 2.10 default layer modes. It is the (red + green = yellow) layer in Linear burn which makes the difference. Dodge is still dodge, although you can tweak the grey colour . White is HSL color mode.
The whole thing is a bit flaky. Best bet use the legacy modes while they still exist.