GPU usage varies between 30-90 in games such as CS: GO, BF5, Valorant. It never remains stable at 99%. So it's constantly changing between 150FPS and 400 FPS, and that's a very wide range. I think the video card is throttling its own power to avoid unnecessary heating and fatigue. Usage in games like RDR 2, AC Valhalla is stable at 99%. Is there such a setting if I want it to use 99% in every game? My processor is R5 3600X, I use the system at 2K resolution.
What you are experiencing is a common problem (driver issue) with AMD Radeon RX6xxx GPUs.
Not much you can do currently, except waiting for AMD to fix this issue with one of its upcoming drivers.