Try setting PBO to disabled (default is auto) and setup a slightly more aggressive custom fan profile for your CPU fans, then use Ryzen Balanced OR a custom Balanced power plan with its minimum processor state set to 85% or lower (Higher for slightly better performance, lower for better idle temps). The clock speeds going down bellow 2200mhz is pretty normal and it does this to save power and lower idle temps, my 3900x for example goes all the way down to 500mhz at idle when nothing is in use with all but 2 cores in sleep mode, you can play around with the minimum processor state to see what fits your needs while testing, 85% was the sweetspot for me during my testing so you can start from there (the default High Performance Power Plan has its minimum processor state set to 100% btw) Also be mindfull of backround programs/processes that may prevent your cores from entering sleep mode, Wallpaper Engine for example is one of them. Only other option to lower temps and prevent it from jumping up and down like that all the time is to use a 280 or 360mm AIO like what i did.
Having all cores enter into sleep mode almost never happens since windows is gonna need one or two cores atleast for its backround processes/services etc, the most cores ived seen enter into sleep mode on my 3900x is 11 of its 12 cores on a newly formated clean windows install at running at idle.
Also you should be using Ryzen Master for monitoring Ryzen CPU state instead of HWinfo, since HWinfo (as of its current build) just isnt able to show you when/if cores are in sleep mode and isnt as accurate as RyzenMaster especially when it comes to Ryzen 3000 and above CPUs.
Not that you cant use Hwinfo at all though since there are some newly added stuff there that are very usefull like Power Reporting Deviation which you can use to tell if your motherboard is running everything up to AMDs spec, it should be as close as possible to 100%, for comaprison My MSI x570 board has its Power Deviation at 101-102% under load and 200-300% when idle which tells me its within AMD spec, anything lower than 90% and the board is running it sligtly overclocked or that you have some Auto overclocking settings enable in the bios and using that info you can tell whether or not you can still overclock your CPU or if there are still some settings that you can tweak.
