Newer versions of iwd has supported connecting to hidden networks for a while now. There's a separate "connect-hidden" command in iwctl that needs to be used instead of the regular "connect" command. The equivalent on dbus is to use ConnectHiddenNetwork instead of Connect.
This change disabled the explicit check that disallows even attempting hidden networks when using iwd and also changes "Connect" to be either "Connect" or "ConnectHiddenNetwork" based on if NM setting says it's a hidden network.
This allows me to connect to my hidden network (via NM using iwd) that I had been previously connected to using NM with wpasupplicant. eg. client / station mode.