I don’t think unique local addresses require manual configuration. On linux at least, I get an fe80:: address derived from the interface’s MAC address even if there it can’t find any router. If the host receives a router advertisement, it will add a local address (the same suffix as the fe80 but with a fd8b:something::/64) and the “internet” 2003::.
I’m not an expert and this may be just the configuration of my router, but all my linux installs automatically got these three addresses without manual configuration or issues.
Yeah, I guess my router just decided on an ULA prefix on its own. Thank you for providing the right terminology and explaining how a host gets these addresses.