@SOSOTE
You can have that network diagram when running Deco mesh in Access Point mode. For TP-Link Deco specifically, "Access Point" means Deco will provide WiFi mesh with intelligent node connection, seamless device roaming between nodes and central single point of WiFi mesh configuration which is Deco app. Internet provider modem/router will manage LAN (IP address allocations, DNS, DHCP, etc.).
In that respect, Deco "Access Point" mode is not the same as generic WiFi Access Point. It is true WiFi mesh with LAN management offloaded to modem/router.
I have three Deco nodes hardwired to ISP modem/router, running in AP mode, I can guarantee it works just like WiFi mesh should.
--------------------------
In regard to SSIDs you want to have:
1. Separate 2.4 GHz and 5 GHz SSIDs for main network.
You won't have this. Deco mesh runs single Main Network SSID for dual band. What I would recommend is run Main Network on 5GHz only and connect all 2.4GHz devices to IoT network.
2. 2.4G or 5G Guess no access to the other networks.
You can have this. You can have isolated Guest network and you can configure it to be 2.4 GHz only, 5 GHz only or dual-band. Note that for Guest Network ISP modem/router is default gateway, DNS and DHCP server. Which means, at least in theory device on Guest Network could access ISP modem/router WebUI. You can deal with that by configuring strong password on modem/router and/or by restricting which IP addresses can access management interface.
3. IOT 2.4G separate network
You can have this.
---------------------------------
One more thing about TP-Link: they have many Deco models and these models are not consistent with feature set. For example, some offer IoT network, some don't. If you have specific Deco model in mind, I might be able to check for you if it provides IoT network. If you haven't, I may be able to provide recommendations, depending on your expectations from Deco nodes, such as: WiFi protocol you want supported (WiFi 6, 6E, or 7), ISP modem/router Ethernet ports speed (gigabit or higher), speed of Internet link.
