What’s the point on the email category (iOS and macOS)

Poison

But why do you hide those necessary settings and don’t give us the possibility to search in those categories?

I'm not entirely sure I follow. You should be able to search and find the information you've stored in 1Password regardless of what category it is in.

Not only for webmail but also for the apps?

There is no mechanism on macOS for filling such information into non-web browser apps at present.

I really don’t get the point on that.

1Password is still a safe and convenient place to store such information, despite the fact we cannot fill it.

When you do a fresh installation of e.g. Spark it will ask for your server settings and password.
There’s no way to access those information but copy them one by one from mail category to the necessary fields.

You can also drag and drop from 1Password into Spark, but as I say there isn't any way we could fill this information automatically with the technology currently available.

Does that help answer your questions? Please let me know. If I'm not understanding please feel free to rephrase.

Ben