RFC 8106 compliance - DNS through DHCPv6 not prioritized over DNS through RA
As per RFC 8106 https://datatracker.ietf.org/doc/html/rfc8106
Section 1.2. Coexistence of RA Options and DHCP Options for DNS Configuration and Section 5.3.1. Procedure in IPv6 Hosts
The DNS options from RAs and DHCP SHOULD be stored in the DNS Repository and Resolver Repository so that information from DHCP appears there first and therefore takes precedence. Thus, the DNS information from DHCP takes precedence over that from RAs for DNS queries.
However, while testing the latest NetworkManager version 1.32.12 (atleast latest available in Tumbleweed) I do not see this happening. Generally I notice that the DNS available from RA appears on top of the one from DHCPv6.