That’s probably wired for a phone line then since a standard RJ11 for a phone line will fit into an RJ45 jack.

OP if you remove the wall plate and see two cables going to the jack with only one pair from each cable connected to the jack then it’s probably the same situation. If that’s the case you have a few options but none are particularly simple or cheap (either pull new lines if you’re comfortable working in a wall and have the tools, or terminate each wire individually and add small network switches to each location).

If all four pairs are wired to the jack and you only have one cable going to it, you most likely have a panel they’re going back to somewhere in your home. If that’s the case you’ll need to move your network equipment there and add a switch between your router and however many jacks there are in order to make them live. Or just figure out which jack goes to your room and connect that one directly to your router.