Your rule only stops pings to the firewall itself. Is that what you are testing?
If so, enable logging for default pass rules to see which rule applies before your block rule.e.g. ICMP v6 is enabled by default in floating section.
NoteWhen changing rules, sometimes its necessary to reset states to assure the new policies are used for existing traffic. You can do this in Firewall ‣ Diagnostics ‣ States.
If a connection is already established due to the ruleset, a new block rule will not apply until the connection is closed. Then the new block rule applies and a new connection cant be established.Reset states forces all connections to close.Reset states for pass rules is not necessary, because a connection cannot be estabslished before, so there is no state "overriding" the new rule.See also https://docs.opnsense.org/manual/firewall.htmlQuoteNoteWhen changing rules, sometimes its necessary to reset states to assure the new policies are used for existing traffic. You can do this in Firewall ‣ Diagnostics ‣ States.