This is an issue with MacOS Big Sur - but maybe Catalina too? Whether it is something that the Graphisoft programmers could have programmed around (to give them priority over the keystrokes), I don't know...
Nothing I tried could get it unassigned from the dock functionality... and so ARCHICAD never even receives the key strokes.
The workaround is to assign a different shortcut to the command via the ARCHICAD Work Environment. In the attached, I'm about to assign cmd-shift-D to the command. Afterwards, that shortcut works fine.
One of the forum moderators • AC 25 USA and earlier • MacOS 11.6, iMac Pro