Thanks for the detailed explanation - so if I understand this correctly, basically there is a port speed and there is an internal bandwidth speed - a port speed could be 100M, 1G, or 10Gbit, for example, but the internal bandwidth should be much much larger than that.

My follow up question is then: if I have a ISP modem -> router A and ISP modem -> switch -> router B connection set up (both connecting from the same ISP modem but using different ports on the modem) and all my PCs/game consoles/smart TVs are connecting to router B and all my IoT devices are connecting router A, in terms of the speed for devices connected to Router B it should, at least in theory, enjoying whatever bandwidth that’s not used by the IoT devices in router A (which I assume would be minimum) and if I only have one PC turned on and that’s the only device connecting to router B then my PC should almost have the same speed as the minimum of all port speed and my internet speed? Is that correct?

Thanks a lot, yes indeed that’s the question I have but I wasn’t just not sure how to ask it. So if I understand it clearly, roughly speaking if there is a device on the switch that saturated the pipeline then all other devices are slowed, but in router with the QoS settings you could guarantee a minimum bandwidth for each of the device? So if I do not use any sort of QoS settings would that essentially make router almost like a switch in terms of routing traffic? I understand obviously routers these days have a lot more functionality like VPN gateway or printer server but let’s just ignore those for the sake of discussion.