To get notifications of all topics, I’d suggest deleting all of those category-specific rules, and then adding a single ‘all categories’ rule.
Can you share some more detail on what you’re seeing here? Some screenshots or a video would be great!
When editing a ‘rule’, you should be able to use the category dropdown to choose ‘(no category)’.
Once saved, it should look like this:
(‘no category’ in the dropdown is clearly a bad description of what it actually means. I’ll get that fixed up)
I think subcategories are ommitted from the help text for space. But you can still subscribe to categories by using their ‘slug’ (the name of the subcategory from the URL). So in the case of #howto:admins here on Meta, it would be /discourse watch admins.