What HDMI cable are you using? Have you tried buying a 4K UHD cable like this?
HDMI Cable 10 FT (4K UHD HDMI 2.0 Ready) - Braided Cord - Ultra High Speed 18Gbps - Gold Plated Connectors - Ethernet & Audio Return - Video 4K 2160p HD 1080p 3D - Xbox PlayStation PS3 PS4 PC Apple TV https://www.amazon.com/dp/B01CRA11IU/ref=cm_sw_r_cp_apa_bi.TAb6TAH9PV
Y’all wanna know something weird? I bought this 15 foot HDMI cable two years ago and it supports 4K 120 FPS perfectly despite it not being an HDMI 2.1 cable.
HDMI Cable (4K 60Hz, HDCP 2.2, HDR, 18Gbps) with Braided Cord, 10 Feet https://www.amazon.com/dp/B01CRA11IU/ref=cm_sw_r_cp_api_glc_fabc_zyD1FbMRGHW5R?_encoding=UTF8&psc=1