Keep my Apple ID, but delete individual iCloud services and data (for example the mailbox @icloud.com) When I type in DuckDuckGo something like How to permanently delete an Apple ID account I get lots of hits. But it will delete the complete Apple ID. 


I wish only to delete the mailbox @icloud.com and @me.com. I no longer wish to have an Apple provided mail service.
I also wish to delete my account (and all data) on individual iCloud services (example iCloud Keychain).
This is impossible as clearly stated on Apple's website:

How to change your Apple ID if it ends with @icloud.com, @me.com or @mac.com
If you use an @icloud.com, @mac.com or @me.com email address as your Apple ID, you can’t change it to a third-party email address.

That is your Apple ID so you can't change it, the only real alternative is to create a new Apple ID.