System I am trying to create

Internet/ModemRouter                ->  SG105E    -> Vlan 2 ( port 2)   -   User xxxxxx, own network
                                                                           -> Vlan 3 (port 3,4,5) My Network     Wifi and guest wifi

                                                                                            Port 3 -> to Deco S7 Mesh wifi

                                                                                            Port 4 -> dumb switch and PCs, printers

                                                                                            Port 5 -> IOT

My Supplied Modem Router has Wifi turned off as I want to use the Deco S7


The Modem\Router has no Vlan support

Can I use the SG105e  to create a simple isolation via a VLAN

Port 1 to Modem

Port 2 to User XXX

Port 3,4,5 My network including Deco S7



Reading up I have believe I can not use the "Port Based Vlan" so Q Vlan using Untagged ports ?

Does this seem correct , lots of sample, then lots of comments that argue the point, so I am confused about what will work and what will not.