Kleopatra "Sign As" has no comment for the key

Ok. The “Ecnrypt for me” has short info too. Only “Encrypt for others” has a long info.

There is Certificate “Conny Comment” on your screenshot.
UID name: “Conny Comment”
UID comment: “This is my key”
UID Email: “foo@bar.org

So. you cant see UID Coment in list, only in popup window.
Try add this uid in to “Encrypt to others” and you will see your comment “This is my key”