It’s a great question!  To use keyboard shortcuts instead of dragging your mouse, try clicking F1 to bring up the shortcut keys and see if one is applicable to your question (on my Mac, I have to click Fn F1). I see a few options for drawing lines and connecting Lines to shapes.  That said, I’m not sure if this will solve your question, but hopefully points you in a helpful direction

Hi ​@Ricardo Ramirez 

Thanks for your post!  Unfortunately, this isn’t currently supported in Lucid, but Lucid is very interested in your feedback and committed to continually improving our products. Please first search the Product Feedback section of this community (with the filter Topic Type = Idea) to see if it’s already been submitted. If so, please add any additional details you’d like and upvote the request - this consolidation helps to refine feedback and properly capture the popularity of the request. 

If no one has submitted this idea yet, please create one of your own and be sure to include details about your use case or what you’d like to see in this experience. One of our Lucid Legends suggested that a simple solution to implement might be to select both shapes (ctrl + Click or mouse selection) you want to connect and a new menu option for ‘connect with a line’. Raising your suggestion will allow other users with similar requests to discover and upvote it, and add details of their own. Finally, for more information on how Lucid manages feedback via this community, take a look at this post.

A possible immediate work-around is to use the Connector object, which is a standard diagramming technique when wanting to connect objects across diagrams or even between diagrams. The benefit to this technique is that it reduces the ‘noise’ of long lines that a reader may find difficult to follow: 

All the best,
Craig