Unfortunately, you will have to add an additional step now. I asked and found out that the old feature won’t be returning. At the top of the filter’s parameter selection box, there is a copy command button next to the reset parameters button. Use that to copy the command to paste it as your new layer’s name.
Thinking about it some more, the new button permits more use cases. One could paste the command anywhere, including in the CLI or layer name field. Also, “Apply to new layer” only exists in GIMP. Krita doesn’t allow that; the old option would not make sense.
A small note about this “feature removal”.
Some filters in G’MIC actually generates several output layers with slight variations in the name (see e.g. “Smart Coloring”, “Drop Water”, “Illuminate 2D Shape”, …).
There are even some of these filters that can be called multiple times, using the output layers generated at the previous call. When this happens, the filter is able to recognize the meaning of each input layer thanks to their custom names (e.g. with a prefix that has been added to the layer name).
The option in the plug-in that sets the G’MIC command to the layer names just broke that possibility, leading to bugs in the way the filter work, just because the layer names are not those expected.
So the same filter may work or not depending on the “command to layer name” option enabled or not in the plug-in. This was not acceptable.
Thus the replacement of this feature by the “copy command to clipboard” button.
Good point. I neglected to mention that because I haven’t had good luck with layered output… (My shortcoming; nothing wrong, as far as I know, with the existing code.)