Best way to disable IPv6 advertisement only to specific clients?

[mkx]

You can’t block advertisments to some clients at the source, being multicast they are sent to all devices within a layer2 network

Just to double-check, is it possible to block on L2 level via /interface ethernet switch rule, or multicast cannot be blocked per client (per MAC) even there?

It might be possible to filter (certain) multicasts on bridge port. But if there are multiple hosts behind that port, none of hosts will then receive filtered multicasts.