You are confusing unique local adresses and link local addresses. Unique local adresses can only be configured manually or, in theory, with DHCPv6. On Debian, I edit the file “/etc/network/interfaces.d/<interface name>”:

• auto <interface name>
• iface <interface name> inet dhcp
• iface <interface name> inet6 static

•     address <unique local adress of your choice within the official range>
  

•     autoconf 1
  

•     accept_ra 2
  

•     privext
  

This gives you: autoconfigured IPv4 address, autoconfigured (slaac) IPv6 address, an IPv6 unique local address, temporary IPv6 adresses (privacy extensions) and your IPv6 link local address.

Yes, your ISP provides you a large quantity of adresses. Not really, the adresses has several parts. Your ISP provides you with the prefix. Your devices complete the rest of the address automatically. You can also use a DHCPv6 server, but I don’t and some devices don’t support it anyway. Yes, all those adresses are globally routable, they are “Internet” adresses. You can still use locally routable adresses too if you want, called Unique local address (look it up on Wikipedia), but that requires manual configuration.

If you don’t use IPv6, you are behind. For me the transition was so hard, it’s a big step behind me, wouldn’t want to do it again.