Hi @k_wullstein - I see that you have an archived Feature Idea on this same topic, and the answer that stefaniesanders gave you there applies here, as well. I encourage you to vote "up" this Feature Idea: https://community.canvaslms.com/ideas/4636-modules-within-modules . Unfortunately, this is not currently possible in Canvas and, as you state, nor can you indent modules.
As you likely already know, you can indent virtually everything else, including text headers. While I realize this still will not completely do what you are after, you might consider adding some text headers to more clearly delineate your lessons. I did this in a sample course site, below. (And actually, what you are seeing indented have been indented twice, since the titles of assignments otherwise do not line up quite the same way:)
I guess encourage folks you know to vote that Modules within Modules idea linked above "up." While Canvas notes it will not be developed in the near-future, that's not saying it won't happen at all.
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