Can I make computers in this subnet visible to computers in the main network without merging them

The problem you are facing is caused by the router on LAN B. It performs NAT, which you don't want in this setup. All traffic from LAN B to LAN A within LAN A has the source address of the router in LAN B. You want a router that only forwards traffic between networks, not translation.

Check the manual for your router to see if you can disable NAT. If not, try to find a router which doesn't have NAT. Most SMB and branch routers have this functionality, you could pick up an out-date model on eBay for USD 50-100. Alternatively as a workaround you could set up port-forwarding (there are many good guides online).

Static route is the main method, but you're not getting the right parameters.

• A route tells the first router that a certain subnet is reachable through the 2nd router – which means the "gateway" must be the 2nd router's IP address from the 1st router's perspective.

  So in your situation, "Gateway IP" must be 192.168.0.x address belonging to the Archer's "WAN" interface, since that's the one directly attached to D-Link.

• As for the "Destination" address, 192.168.1.1/32 isn't wrong, but it is also not very useful: it only lets you reach the 2nd router itself, but not the remainder of the 192.168.1.x subnet.

  In most cases, you would want 192.168.1.0/24 as the destination instead.

(Why were your attempted gateways wrong? Well, 192.168.0.1 won't work because that's the first router itself, and telling it to route something through itself would just create a tight loop.

And the 1st attempt, 192.168.1.1, won't work because the D-Link doesn't know where that address is yet – after all, you're just adding a route to it right now; it's a catch-22.)

Finally, even after configuring the right routes, remember to check the Archer's firewall – very likely it will be blocking inbound connections by default.