It's not a routing issue, it's a firewall issue. Make sure you have a proper firewall on your network and don't rely on fake firewalls like ufw if you're concerned about this.

Again, if your router or perimeter devices are appropriately managing your network then it's a non-issue. By default most home routers have IPv6 disabled, and if you're setting up an enterprise environment with a VLAN you're probably subnetting IPv4 instead of using IPv6 at all.

All that means that if you're using IPv6 then you're proactively enabling it on whatever is handling your perimeter, which means you hopefully know what you're doing along with all the gotchas that come with that setup.

Most modern equipment bans inbound traffic that doesn't match an existing outbound traffic flow