I also faced the exact same problem. Unfortunately there doesn't seem to be that many online resources for this field, and the existing ones aren't really that good (e.g. the one by Leiden University, like many other MOOCs, is just way too superficial and brief).
My suggestion is just to find good textbooks and read them. When there wasn't any MOOC online, programmers also learned a lot, by reading good materials. In fact I'd say they're likely to be more reliable than MOOCs in a lot of aspects, since top-quality MOOCs are really few, but you can pretty much guarantee that textbooks widely used and reviewed are written with care.
Here are two that I personally have used:
- Contemporary Linguistics: An Introduction, by Katamba, O'Grady, Archibald, Thomas: This is also used by the program at my current university to teach freshmen.
- The Cambridge Encyclopedia of Language: Not really an introduction textbook, but presents all topics in linguistics concisely in all-color format. I found it generally easy-to-read and enjoyable.
You can surely find other books by searching online.
Of course you might argue that those resources aren't free. But I guess you have to realize that the current proliferation of free materials in programming is really not a norm yet in many other fields. And even in programming, to find really good materials you usually have to pay anyways.
