Accessing USB flash drive network storage and printing with 2 different subnet network and routers

According to the previous thread you mentioned:

Can the B3000 and AX1800 ping each other, including any of their devices?
Example, can ping 192.168.10.121 on the 192.168.8.120?

If the WAN -> LAN enables the forward to accept on the AX1800,

and configure add the route rule on the B3000,

The device from B3000, can ping to the device on AX1800, means that
192.168.8.120 - Device that needs to print
is able to access
192.168.10.121 - HP Printer