Try using a wired connection to speed test.Verizon.net
That willl show what your true speed is.
You mention modem router pc.
FiOS does not use a modem. Only a router.
Do you have one device from ont or two?
Ont is device that connects to fiber.
Ont is box typically outside your house that takes fiber and splits out internet and TV or phone if you have them.
ONT=outside network terminal?
3rd network diagnostic test for download is 12.64Mb/s
"This connection is sender limited 84.39% of the time". Is "sender" Verizon?
My ethernet cable is cat 6 pc/router/jack/ont.
Optical Network terminal. I.e the box wire the FIOS Fiber (optical) connects and is converted to several type of wire connection (phone, Coax, and ethernet)