I currently use iwd with NetworkManager on a couple laptops running Arch
Linux. I also am working on an RPI project with connman/iwd managing
network interfaces. Currently, if we use the connman interface to scan with
iwd, we never get a return:
"connmanctl scan wifi" just hangs and requires a ctrlC.
This was noted on the Arch connman page:
https://wiki.archlinux.org/index.php/ConnMan#Error_/net/connman/technology/wifi:_Not_supported
On my rpi project, we are using nginx/php to set it all up and we use the
'iwd station wlan0 scan' then 'connmanctl services' to select SSIDs. I
asked on the connman list and Daniel says that connman is waiting for a 0.

Scanning is supported with iwd. connmanctl scan is probably waiting for iwd
to respond with the scanning=0 signal. If iwd doesn't send out this signal
then this will hang.

Don't know if it is a connman or an iwd 'issue', but wanted to bring it up
here to see.

Keith