Perhaps I can improve this a little.

SLAAC is for stateless assignment of an address without dhcp. It's what android uses exclusively for example. Delegated prefixes (/64) can be assigned by SLAAC or DHCPv6, and openwrt works with either. OP's provider may not even use SLAAC, or at least make it secondary since SLAAC and DHCPv6 don't always play nicely.

In the case of privacy extensions, this is up to the clients. Some clients might even not use them. Global temporary addresses are an attempt to stop fingerprinting. They're largely ineffective these days however. Importantly, that temporary global address is still globally accessible (remember, there is no NAT), although most OS's will ignore incoming connections. Otherwise, correctly, clients should have a couple of ipv6 global addresses.