So here is my network setup, I have my network ISP’s modem/Wifi AP, a switch (TP link TL-SG108E) and a router (D link dir 600M).

I have 150Mbps Internet connection.

The WiFi access point is on the Modem provided, and it always has 4 phones connected to it.

The switch is connected to the modem.

The router is just an old one lying around and is used to extend wifi to another room without coverage, and is connected to the switch via LAN.( I have set it to use different channels for optimal connection. So that’s also not the problem).

My TV is connected to the Switch by LAN, but it only supports 100Mbps LAN.

The problem is whenever I switch on the TV the wifi speed drops no near nill on all the devices connected via WiFi. The problem persists even when TV is not using any bandwidth per se.

I would also like to note that I get the whole 150Mbps speed while downloading from say Steam/Epic. (My laptop is connected to the same swich vis Gigabit LAN), so it is not an ISP issue.