Only object mode is available when selected stroke, in 2D animation

I am a beginner to 3D, and blender. I usually draw.

I arranged some cubes in another collection.
I select stroke in the outliner.
I can’t draw, or jump to any other key frames - ‘no more key frames in this direction’. I can’t do much else in object mode.

I saw another post with the same problem, but he selected the camera by mistake or something. It’s pretty obvious I’ve not done that.

could you send a screen with the outliner, or even better a blend file?

Capture

have you solved your problem already?

No. I’ve given up for the moment.