On a much older version (debian stable's 1.3.3-2), replying to f.e. SMS notifications, the »send«-button had an accelerator on the S, allowing to send a reply with ALT-S. In recent update of kdeconnect to 20.04.2-1 (debian unstable) that has gone missing. Is it enough to add an ampersand to line 41 of kdeconnect-kde/plugins/notifications/sendreplydialog.cpp as in ` button->setText(i18n("&Send"));` ? If so, would be great if someone could add it : )
The pop up window described (sendreplydialog) has been replaced in favour of reply-able notifications, which are provided by KNotification and should support all the relevant accelerators, etc.