Ah yes, good find: the stroke node can only apply to vector data, but when you use the Circular Repeat node, it now produces group data (as it should have always done). The fix is to put the Stroke node first to avoid the type error. I'll see what I can do to update the tutorial with that info, and to try to make the Stroke node more robust so it could apply to all group elements.
I'm surprised that Ctrl+Z undid more than one step, I've never seen that before. If you get the chance to reproduce that and write up the steps, please file an issue since we'd like to take a look into that.
I can try to reproduce but don't want to go through all the steps every time in case things go wrong again. Is there a savepoint/export/import kind of feature?
I think a tutorial regarding basics such as how to find shortcuts, do's/dont's for new beginners might help.
You can save the document and reopen it later just like in any other program. You might not be able to reproduce the graph validity error anymore because we fixed the specific bug you encountered. The input hints bar at the bottom shows what buttons you can press in any context, but that's a good idea to mention it in upcoming tutorials because I've noticed that users tend to ignore it. Hover tooltips and the app menu also both display shortcuts, which are worth pointing out in future tutorials as well. Thanks for that suggestion.
I'm surprised that Ctrl+Z undid more than one step, I've never seen that before. If you get the chance to reproduce that and write up the steps, please file an issue since we'd like to take a look into that.