I am able to duplicate issue after connecting display LG Electronics UL TRAGEAR with refresh rate 179.96 Hz on below configuration setup –
Alienware Area-51 R6 + AMD Ryzen Threadripper 1950X 16-Core Processor + Ubuntu 20.04.3 LTS + 5.4.0-81-generic + Driver 470.63.01 + NVIDIA GeForce RTX 2080 + BenQ EL2870U with 60 Hz + LG Electronics UL TRAGEAR with refresh rate 179.96 Hz
I have filed a bug 3423370 internally for tracking purpose.