The title says it all - in settings of the trashcan applet, there is no possibility to set a shortcut - the shortcut would open the trash in the default file editor. Of course one can set up a custom shortcut launching for example "dolphin ~/.local/share/Trash/files", but that is more technical than neccessary.
Would be fixed automatically if we implement Bug 446548.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/1656