systemd version the issue has been seen with

245.4-2

Used distribution

Archlinux

Expected behaviour you didn't see

Most networks will be ipv4 only for quite some time. When an ipv4 connection is available, systemd-networkd-wait-online should continue, instead of waiting for a possible ipv6 RA. This is even more true when DHCP=ipv4.

Unexpected behaviour you saw

My ipv4 only network connection takes ~ 16 seconds to be available according to systemd-networkd-wait-online. However, roughly half of that time is spent waiting for an IPV6 RA:

14:32:57 systemd-networkd[542]: NDISC: Sent Router Solicitation, next solicitation in 7s
14:33:05 systemd-networkd[542]: NDISC: No RA received before link confirmation timeout
14:33:05 systemd-networkd[542]: NDISC: Invoking callback for 'timeout' event.
14:33:05 systemd-networkd[542]: enp8s0: State changed: configuring -> configured
...
14:33:05 systemd[1]: Finished Wait for Network to be Configured.

Steps to reproduce the problem
Have a network without a router performing ipv6 advertisements. Configure your .network with DHCP=ipv4. Without adding IPv6AcceptRA=no (which should not be required) the interface will take ~7s longer to become configured