You relise the base frequency of a 5900x is 3.7ghz, the cpu will always default back to that, at idle, if your hitting the cpu with a heavy workload the clocks are genreally lower anyway as temprature would become a factor at that point, normal behavoir of am4 chips is from base clock (3,7ghz) to around 4 - 4.2ghz, gaming loads should get you around 4.4 - 4.7ghz region as more cores are being used.
Unless you do a manual overclock the boost frequency on a 5900x is indeed 4.8ghz but thats only on one core, out of the box the cpu will never hit all core 4.8ghz, tempratures would shoot up too fast and the cpu would throttle back hard.
As others have stated am4 loves ddr4 3600mhz, with tight timings, (cl14/16), going past 3800mhz on ddr4 will introduce more latency which in most cases hurts performance of the cpu and most tasks in windows, you'll know as games will keep crashing, windows will bsod or lag/freeze.
I would have a look at your cpu temps at idle and under load, if the cpu is stuck at base that could be a overhating issue, the cpu's protecting itself.
the 5900x has a max operating temp of 90c if your at that or close the cpu boost frequency is always lower because temps are too high.
looking through your speccy link i can see your motherboard bios version is 1.4 dated 11/8/22, thats far too old, i would look at updating it to bring all the agesa updates which will probably make your cpu run faster than 3.7ghz.
OP's using Team Group - UD4 3200mhz ddr4 modules (4*8gb kit)
