This Youtube is about 2
separate LAN networks.
You got what you looked for.
This is only just one limited way of setting this up.
You can have "n" WAN and "m" LAN in any Mikrotik. With "n" and "m" a number between 0 and some high number.
WAN and LAN, used, separated or interconnected just as wished.
Please consider:
You have 2 LAN subnets, how is routing set up between the LAN subnets? 2 IP subnet even when on the same L2 network (bridge, ethernet, whatever L2) do not communicate in L3 (IP) without routing.