@phnt it works from that wireguard host

$ ping 15.204.35.21
PING 15.204.35.21 (15.204.35.21) 56(84) bytes of data.
64 bytes from 15.204.35.21: icmp_seq=1 ttl=63 time=32.7 ms

the route is working, it goes over the tunnel

It's just that traffic from the outside world that hits that host's NIC should be forwarded by the kernel over the wireguard tunnel. It's just not even trying. But it SHOULD. The route is there.