I used to be able to use the paint bucket to change the color of a sky and then the brush tool to fill in all the tiny areas around the trees easily because the brush only filled in the sky and did not color the branches. All of a sudden I can't do it anymore and I don't know what has changed. I don't remember pushing any buttons.
What OS and version of Elements are you using? And what is it that you can't do any more? What happens when you try to do whatever it is you are trying to do?
If you have any interest, Elements 2021 which was just released has an automatic guided edit to replace skies. If you don't want to upgrade, there are also many better techniques for changing the color of a sky than using the paint bucket and brush.
Try this alternate advanced technique. You will need a picture of a "good" sky - - just blue sky with clouds, nothing else on it. You can take it yourself or obtain one from another source, e.g. Google photos.
1. Open the picture with the drab sky (A) and the picture with the replacement sky(B)
2. With A open in the work area, copy/paste B. B will come in on a separate layer. Activate the move tool and position B over the entire sky in A, including the tree branches. Change the blending mode of the layer with B to darken.
3. Set the foreground color chip to white.
4. Activate the gradient tool, and select the foreground to transparent (linear) gradient. Once you have this, drag the gradient from the bottom of the picture to the top of the tree canopy while holding down the shift key. (South to North)
5. With a soft, white brush you may wish to paint the horizon a tad to make it lighter compared to the rest of the sky.
6. Suggest that you work on a copy of your original file until you have mastered the technique. This process beats trying to paint between the fine arborization of a tree with leaves on it.
7. I saw this described some years ago by someone named Alibony, and the credit should go to him or her.