I searched but could not find a duplicate.

I want to apply a modifier to only some parts of my animation. My idea was to create separate stroke objects (Add -> Grease Pencil -> Stroke). However, I cannot seem to easily switch between which stroke I'm drawing with. I did manage to do it by accident, and now if I select the different stroke in object mode, I can draw with it later. But that's a lot of work to switch strokes.

Selecting the different stroke in the outliner does change the timeline data so it corresponds with the new stroke, but does not switch the materials, and does not let me draw with it.