@Blitz357,

From my understanding, you should be able to accomplish what you are doing with no problem. You could, if your situation allows, move the switch to the other room and split the ethernet connection equally to your PC and Deco, however, your original setup should work great.

On your desktop, if you navigate into the network adapter settings, and then find its properties; you will be given the maximum speed that the PC can send through the line, given the way it auto-recognized the setup. If you have a link speed listed below 1000Mbps, you should either replace the ethernet cable, or check the auto-port negotiation settings for your PC's network adapter.

I believe that the next major step down in speeds from the 1000Mbps standard, is in fact a 100Mbps maximum, which would line up with the speeds you are listing. I would also recommend changing the QoS settings in your Deco to either be disabled or to have a manual speed assignment that is greater than what you are expecting to receive from your ISP.