Bug/feature?! Can only start a new chat/add contact via DC special link or QR
it is a feature 
first, if you’re not using chatmail but a classic mail address, you can contact ppl using the email address.
for chatmail: as chatmail does not allow sending unencrypted messages, options resulting in “cannot send” at the end are tuned down/removed from the beginning on - that way, one can find the paths that are actually working - as the mentioned links or QR codes - or, pretty new, vcards
there are discussions to be less strict, see eg. don't prevent creating contacts without keys · Issue #3361 · deltachat/deltachat-android · GitHub , but in general, it is on purpose.