I have 2 shots of a landscape one with the sky exposed well and one with the foreground exposed well but the sky is washed out.
I’ve noticed when I have tried this in the past it goes something like this:
load the images as layers
remove the sky by painting or by select by color and allow the sky to show from the lower layer.
However, I almost always end up with a ‘halo’ around my sky, or I end up painting because selecting by color does not allow me to paint only my selection with white
In GIMP you can apply a layer mask to the brighter image which lies above the darker one. When you select grayscale copy of layer as the mask, the bright sections become more transparent than the dark ones, letting the dark layer shine through.
Then you may adjust the brightness curve of the mask to your convenience
I often blend images like this using a gradient mask (paint the mask from black to white with the gradient tool). This replicates the use of a gradient filter placed in front of the lens.
Another option is to create a mask using the threshold tool to select the sky or foreground, but feather the edges well to avoid a halo.
There are numerous commercial programs such as Lightroom, Zoner Photostudio and others that handle this problem well. I have never tried Enfuse, but that sounds worth looking into. However, the gradient mask in GIMP is my favourite way to blend the sky if the horizon is flat enough to facilitate this technique.