Yes, these things are possible, but highly non-trivial.
Documentation is at https://docs.edx.org/ , in edx-platform itself, and on each installation of edx at /api-docs/ e.g. https://courses.edx.org/api-docs/
One example is the Open edX mobile app - it interacts through the platform entirely through APIs and iframes, so you can check out how it works as an example.
Also, the entire platform is being converted slowly to “micro-frontends” (MFEs), which interact with the platform only through REST APIs. As that work is completed, it will give you more examples of interacting with the platform through API only, and make it easier to swap out the existing MFEs for your custom frontend. At the very least you should find GitHub - edx/frontend-app-learning to be a useful example, as it uses APIs and iframes to display Open edX content.
https://www.labxchange.org/ is another example, which is built using Open edX. It’s closed-source, but it shows what else is possible.