I believe it's not intended that "gl_FragColor Output" can be deleted; it has no ✖️ button to delete the node.
However, you can select the output node and then use "Change Node Type" to convert it into some other node.
At that point, the application state is already broken, as there's no output node anymore.
It seems impossible to turn it back into an output node.
Additionally, the new node type has the ✖️ button to delete now, so it can be removed completely.
At that point, you are left with an empty canvas.
This can also happen when you have already spent a lot of time on a composed shader, which is almost equivalent to data loss (as your shader is corrupted now).
I believe it's not intended that "gl_FragColor Output" can be deleted; it has no ✖️ button to delete the node.
However, you can select the output node and then use "Change Node Type" to convert it into some other node.
At that point, the application state is already broken, as there's no output node anymore.
It seems impossible to turn it back into an output node.
Additionally, the new node type has the ✖️ button to delete now, so it can be removed completely.
At that point, you are left with an empty canvas.
This can also happen when you have already spent a lot of time on a composed shader, which is almost equivalent to data loss (as your shader is corrupted now).