Just "kde" here seems very strange. This should be "kde.org" (or "k3b.org", but the first seems more valid given the desktop filename and appdata filename already live in the "kde.org" domain).

Seems K3B does not use KDbusService, and might also not use KUserFeedBack, so this property might be ignored currently in k3b code and thus not be a problem.
But to protect against future uses and thus fails, and for consistency, I recommend to change this to "kde.org".

(And indeed does not fix the program icon issue on wayland given current KAboutData logic, but @stikonas has already fixed that with 04a19f5e5a3debdce5696459de9b862f649082e9).