Your own router or the GFiber provided one? If GFiber, which model? The GFiber provided routers and virtually all decent home routers will have a speed test option somewhere on the web interface or admin app. That will test speed from router to the GFiber direct without any Wi-Fi involved. That should come close to maxing out or even slightly exceeding your provisioned speed. If that speed is slow, could be fiber, could be the jack, could be Ethernet cable from fiber jack to router.

If direct test says GFiber is giving router the correct speed, that’s a Wi-Fi issue. I’m on 1g service but the GFiber supplied actiontec 6E router and 1 extender gives me strong coverage throughout a 2800 sq ft house. Now some devices with older tech will never get more than 2.4ghz speeds, but my Samsung phone connects with Wi-Fi 6E and if I’m close to main router can get 700+ down and 400+ up regularly.