Adding to this...it also killed CPU core boosting on my 3700X and 5800X systems. And, as noted, monitoring was affected because I couldn't monitor CPU core clocks in MSI Afterburner. Although I could in HWInfo64, strangely enough, which is how I could tell core boosting was effectively disabled. One is on an MSI B450 board but the other on an Asus so this effect, at least, isn't limited to MSI.
I did not suspect this was the problem. I thought it was an effect of my recently updated BIOS so I reverted to one that, as it would have it, did not enable SVM (CPU virtualization) by default. So when I started up after reverting I was happy to see boosting was back to normal... until I enabled SVM manually. That's when I knew it was the problem. So, thankfully it's fixable (sort of): either disable SVM in BIOS or disable Memory Integrity in Windows' Security settings.
I'm sure it's an effective security setting for certain exploits so I guess you should only do this if you're comfortable of your internet security practices otherwise. I also expect it will be re-enabled with subsequent major updates (at least) so anticipate doing this again (disabling Memory Integrity) after they drop.