WiFi Network Isolation and Client Isolation within the WiFi Network

I got myself an Chateaux 5G S53UG+M-5HaxD2HaxD-TC&RG502Q-EA Router running routerOS v7.14.3, which should replace my UniFi Setup (USG, PoE Switch and AP).

The UniFi interface is straight forward and allows the configuration of basic security functions very easily. I need to transfer my UniFi setup to the Mikrotik router where I am currently struggling with the WiFi setup.

What do I have? I have 3 WiFi networks (private, smarthome and guest) with different IP subnets.

What do I actually want?
a) I do want to limit any client of a WiFi network to his WiFi network only. The client must not be able to reach another subnets. For instance, a client connected to WiFi “private” must not be able to reach clients within the WiFi network “smarthome” nor “guest” and vice versa, but is able to talk to other clients within his network.
b) Clients in WiFi network “smarthome” must be completely isolated within their network, that means client A within WiFi network “smarthome” is not allowed to reach / communicate with client B in WiFi network “smarthome”.
c) The WAN / internet must be reachable anytime.

What settings do I need to accomplish this?