Current situation:

If I enter my root domain into the "hostname" field I'm only allowed to create entries such as A, AAAAA, MX etc. but not CNAME.

Wanted situation:

I can create a CNAME entry with my root domain and this will be flattened automatically, like Cloudflare does (https://support.cloudflare.com/hc/en-us/articles/200169056-CNAME-Flattening-RFC-compliant-support-for-CNAME-at-the-root)