Reading the manual for the Logitech K380, it turns out that LPChip's answer is rather incomplete. As I pointed out in a comment, the Fn modifier switches the functions of keys at the level of the mappings from physical keys to actions inside the keyboard itself, and this applies to things like the function keys on row F.
The engravings implied that this was the case for the keys on row A, but this is not so.
Per the manual, the four so-called "split keys" on row A actually function specially depending from the current internal mode of the keyboard. This mode is manually switchable using Fn+I for "iOS" mode and Fn+P for "PC" mode. (Again notice the use of Fn to modify actions at the level of the keyboard itself, modifying these keys to perform internal actions within the keyboard instead of sending USB input reports over Bluetooth.) Presumably a custom device driver for each operating system sends a USB output report to auto-switch this to the appropriate mode at device initialization. (As I mentioned at https://unix.stackexchange.com/a/467190/5132 , vendors sometimes define private USB output reports with this kind of functionality.)
What you are looking for are the left and right "GUI" modifiers (in USB terminology), a.k.a. "Windows" or "Command". As I said, USB is actually platform-agnostic, and all three of these are names for the exact same key at the USB HID protocol level.
- In "iOS" mode there are two and they are the Alt/Cmd ⌘ and AltGr/Cmd ⌘ keys. So Alt/Cmd ⌘+D or AltGr/Cmd ⌘+D are the chords that you want.
- In "PC" mode there is one and it is the Start/Alt ⌥ key. So Start/Alt ⌥+D is the chord that you want.
Each of the three possible Bluetooth pairings apparently has its own independent value for this mode, moreover.
Moral: always read the user manual. ☺