Hello,
If you create a Tilemap and don’t give a source image, when you put it in the Scene, the entier content of it stops to be displayed.
So you also can’t select it, since you don’t have any object drawn.
On the previous Tilemap object, when the Tilemap had an issue, you had a red cross at its place.
GDevelop version : 5.4.207
I can reproduce this, adding it to the scene blanks out everything on the same layer, and then you cannot re-select it for deletion. You can select it from the instance panel, but you cannot delete it from there, so the scene is then broken unless you haven’t saved since. (Undo does not fix this, even if you go back to before creating the object).
That said, there should never be a valid use case for creating an object without the required resources, so for that same reason I’d think it also shouldn’t let you create the object without the required parameters, either.
Basically, the Apply button should be greyed out until you select a resource, in my opinion.
(And invalid resources should show the red X, as the OP mentioned)