Ampere is a terribly taxing architecture.
Gamersnexus had an RTX2080TI running even on a Ryzen 5 1600(Zen1),and they got over 60FPS at 1080p and the CPU was definitely a bottleneck there.
There are videos of a Ryzen 5 2600 and a RTX3060TI(which is far more powerful than an RTX3060):
Even with a CPU bottleneck,average FPS at 1080p are 100FPS! The worst minimums,were in the mid 50FPS range. Zen+ is generally slower than Skylake based CPUs in games such as GTA V.
Unmodded GTA V will run on most modern setups easily - its why its popular to this day.
With the Redux mod,the Ryzen 5 2600 and a RTX3060TI has similar minimums,and the average moves down to 80~90FPS:
An overclocked Ryzen 5 2600/1600AF is equivalent to a stock Core i5 6600 in GTA V:
https://www.gamersnexus.net/hwreviews/3547-amd-r5-1600-af-cpu-review-best-cpu-under-100
The Core i7 6700K and Core i5 7600K have similar boost clockspeeds,but the Core i7 has 200MHZ high all core clockspeeds,so should be under 10% slower than a stock Ryzen 5 3600 in the game.
So looking at the evidence to hand,even with a mod like Redux the performance seems really off.
Its why I suggested to see if there was any crypto malware on the system. The CPU might be thermally downclocking too,and the system is also running the RAM at only 2133MHZ. But even then a Core i7 3770K and GTX1660 are fine with the game,as is the Core i5 7400 and RTX2060 combination.
Plus apparently their RTX3060 is "4GB" - makes you wonder whether they have one of those China special rebranded Fermi GPUs.