BTW, I run both the modem and router from linear power supplies connected to a power line that is dedicated to my network gear and music server in a separate room, and only connected to my main system via a fiber optic line that feeds the Roon endpoint/streamer.
+1 @mitch2 ! Very similar for me, except no fiber. I run a better ethernet cable to my Roon endpoint / streamer. I run this directly through the walls and avoid cheap wall couplers. If I do need to couple the ethernet cable I use these from JCAT:
https://jcat.eu/product/net-isolator-gigabit-network-isolator/