That's a shot in the dark, but I may ask it here: Do you have a simple documentation that would tell someone who knows how to route an IPV4 network and avoid the pitfalls, what is the correct way to do it in IPv6? I struggle to find a good summary of the things one needs to know

IPv6 is weird for someone coming from IPv4. Basically every IPv6 address is a public IP address. Your firewall is responsible for blocking inbound traffic from actually getting to the devices at these addresses. This replaces NAT. So, what I do is have a default rule that blocks all IPv6 traffic inbound. Then, instead of a NAT rule, port forwarding, etc., I just allow inbound traffic on certain ports to certain addresses.