Are you use the details/summary approach? I’d say get the accordions to work with that (as no CSS is needed and it will open and close for you) and then later adding styling like making it look like a button.
I don’t know you’ve generated your listing with code so I can’t comment on much. This is the first time you’re bringing in posts as well. Can you use some generic data YAML file in _data to build up your nested accordion and share that data and HTML?