Wireguard is not a link layer (layer 2) tunnel; it is a network (layer 3) tunnel. It operates at the IP layer. You cannot use Wireguard with any non-IP layer3.
AllowedIPs can be disabled if you want; just set it to 0.0.0.0/0. AllowedIPs is needed because netfilter can't "see" which public key an inbound packet is coming from, so by the time a packet gets to netfilter it's too late to accept/reject based on which peer sent it to us.
> Only one peer is allowed to use 0.0.0.0/0 for AllowedIPs
This is simply incorrect. You can have two peers with the same AllowedIP; you just have to put them on separate interfaces (wg0 and wg1 for example). This is for exactly the same reason that a routing table can only have one default entry. If you want two default entries, make two routing tables.
> Yes but UI wise it presents itself as one
No, it doesn't present itself as one.
> since it’s acts as an interface
So does /dev/net/tun, which is definitely not a layer 2 interface either.
> you just have to put them on separate interfaces
I don’t have to do this with normal data link layers. That’s the point of the complaint. Wireguard is not a true data link layer. Manually configuring multiple interfaces for something I can do with just one interface with a normal data link layer at runtime is an extra inconvenience.
> This is for exactly the same reason that a routing table can only have one default entry. If you want two default entries, make two routing tables.
Using nftables I can specify different routers to use based on arbitrarily complex packet rules. Using just one interface. I can’t do this with wireguard, it will only allow me to to route arbitrary packets to a single peer on an interface. This is an inconvenience.
This is less important although useful in some cases. The more important thing is outbound - since Wireguard is layer 3, in the routing table you can't specify a peer to send the packet to like you can with ethernet, and it has to choose one using AllowedIPs.
AllowedIPs can be disabled if you want; just set it to 0.0.0.0/0. AllowedIPs is needed because netfilter can't "see" which public key an inbound packet is coming from, so by the time a packet gets to netfilter it's too late to accept/reject based on which peer sent it to us.