PS There are two ways to merge layers. The first is to select the layer you want to merge, right click on the layer, and select Merge Layer. The second is to select the merge visible layer under the layer option. You can turn off the small eyes in front of the layer you don't want to combine, and only keep the layer you want to combine for operation

The first

Hold down the ctrl key and select the layer you want to merge with the left mouse button, then right-click the layer and select the merge layer

The second

Click the layer option to select the merge visible layers, which will merge all visible layers. You can turn off the small eyes in front of the layers you do not want to composite, and only keep the layers you want to composite for operation