Hello,
you say:
It's also confusing. In the documentation it says: "Please note, use only the storage
"custom, Article, introtext" for the field "fieldX"."
it's written:
Please note that: introtext in Articles and description in categories should be set in custom format, because it stored integration element for seblod 2.x
this means that if you want to store in the introtext database field, you must use the custom storage. But this don't mean, all your custom field must be stored in introtext.
each field could be store in a new column in database, and if you use the custom storage, use the syntax i describe in my previous answer.
you say:
Stil no fields showing up in when adding an article in the backend.
with the storage you use "custom | article | introtext" you have erase the ID that SEBLOD store in introtext to make integration with Joomla!, so it's normal that nothing work.
Just put the good storage for your fields and it will work.
Regards.
Lionel