How do I clone something from a different layer to another one? Thanks~

According to the documentation:

https://docs.krita.org/Clone

The note about Cntrl-Alt-Click being disabled seems to be still true so you can't do it that way.

If you type 'clone' into the filter field at the bottom of the Brush Presets docker, it should list a clone brush for you to select. This will work on a single layer by Cntrl-Click on the source and then you can clone-paint to another part of the layer (as you'd expect).

To clone to another layer, click on the Edit Brush Settings icon (under the Select menu bar item) to get the brush editing window open.
Expand the Color group (if it's not already expanded) and click on Painting Mode.
Tick the box that says 'Clone From All Visible Layers, then close the brush editing window.

Now, you can clone from anything that is visible, into the currently selected layer using Cntrl-Click to select the source point. There will be a problem if your target layer has content that obscures your source layer but you could rearrange the layers to take care of that, on a temporary basis.
Also, for complicated obscuration problems, you can make a temporary layer as the target layer and arrange the layers so you can clone a region. Then you can put the temporary target layer over the final target layer and merge them.