IWD has supported randomizing the adapters MAC address on startup for quite some time, but this only randomizes the address once for the lifetime of IWD. In the 1.6 release address randomization on a per-network basis was added. Enabling this can be done inside IWD's main config file (default /etc/iwd/main.conf):

# main.conf
[General]
AddressRandomization=network

This option was added to AddressRandomization but truthfully this is not random. The MAC address is generated using a SHA256 digest from the permanent adapters address and the SSID being connected to. This is a deterministic operation which will allow the same MAC to be used on every connection to a given SSID. Generally this is the behavior the average user wants. For fully randomized MAC addresses see AlwaysRandomizeAddress.

The (AlwaysRandomizeAddress) option was added to network provisioning files. Its value only takes effect when AddressRandomization is set to network. When enabled the MAC address is randomized on each connection to a network in a non-deterministic fashion. To the access point it will appear as if a brand new client is connecting every time.

The (AddressOverride) option was added to network provisioning files. Its value only takes effect when AddressRandomization is set to network. When enabled the MAC address will be set to this value when connecting to the network that the provisioning file dictates, and only for this network.

# /var/lib/MySSID.psk
[Settings]
AddressOverride=11:22:33:44:55:66