Packet loss so bad Pc is unplayable

Recently moved into a new spot and bought the most expensive Xfinity internet package 2000 upload/download.

PC gamer so I have an Ethernet cable (100ft) cat6 running from my XB10 modem/router combo in the living room down to the basement. It’s fine maybe 20% of the time with no lag/packet loss but 80% of the time packet loss is to the point every game is unplayable.

I’m talking valorant packet loss spiking all the way to 100% - but usually goes from 0-35ish% every few seconds. Completely unplayable, enemies skipping across my entire screen can’t even shoot.

I’m concerned my coax cable is damaged but I don’t know a lot about internet since I’ve always lived in apt buildings with no issues. I even bought 2 different 100 ft cables bc I thought my Ethernet cable might be damaged but the same issue happens with both.

Anyone have any suggestions… should I buy an extender instead of running that long of an Ethernet cord? Maybe a tp link? Replace my xb10 modem/router combo? Do you think it’s my coax cable?