OK. I tried to embed a simple Desmos graph (https://www.desmos.com/calculator/5kgxq8idfn) into Moodle.
The embed feature failed. I was able to do it with an iframe tag. Here is an image of it: (Attempts to put the code into the description, or alternate text are causing the blog to actually use the code.)
This did not work in WordPress either. It changed the pasted iframe text to what you see below automatically. Following the link does not give you access to the tools to adjust the line like following the link at top does. So I expect that the fault in embedding Desmos graphs into Moodle is partly on both sides. I, however, have my hack above when I want to use it.