If you WireShark this, I bet B is successfully sending packets to A and A’s devices, and A’s packets make it all the way to B but B doesn’t forward it to its own LAN, and it stops there.
Yep that’s exactly what I see.
Can you post the output of ip ro and ip a on both routers? (Feel free to redact your public IP/ISP stuff if it shows up)
I would only be able to for one router. Router A is a tp-link AX73 which doesn’t support OpenWRT. Router B, however, is a tp-link Archer C7 and is flashed with OpenWRT.