I have a simple line added as a layer from a KML file. I can select the features and show numerous nodes. It is in edit mode. Normally I would expect to be able to delete a node, split a line, etc. but none of the advanced digitizing works. The vertex tool is grayed out. I get the error "CAD tools are not enabled for the current map tool". I have scoured Google and am at a loss.
Not probably the correct way to do things but I selected Vector/Geometry Tools/Simplify/Run in Background. This created a new layer titled "added geom info" which I was then able to edit with the Vertex tools. Hopefully someone can answer why I needed to go to that additional step as it is not intuitive. The KML file was created from Google My Maps highlighting a route so it must have to do something with the line being a coordinate or something?
I had same problem- Imported a .kmz polygon and it could not be edited. Solution is to go to vector-Geoprocessing-dissolve. As default, a new layer named 'Dissolved' is created. This can be edited. Rename this to your original file and delete the imported file.
To enable vertex editing your layer needs to have a column set as Primary Key. This is not possible in some data formats.