have a look at everything starting at login/bootup, everything running in task manager (check Processes sorted by CPU usage(, your lower toolbar, etc., and see what might be choking things up...
a Freefixer scan or examining autoruns,will show almost everything... (perhaps some sort of AV scan occurring on startup, etc., could be contributing, but, with NVME storage and an 8700K, that seems a stretch, and I'd not expect any sluggishness, short of a botched or marginal AV app) Anything shown on Freefixer can be evaluated for possible impact, delete things at your own discretion and risk, although most critical processes are 'whitelisted' , ergo not eligible for deletion
If this started quite recently, perhaps a rollback (via restore points) to a point taken a week or a few days ago, etc., might help...
www.freefixer.com
Autoruns may be run straight from MS, note the link that says 'Run now from SysInternals Live'
https://docs.microsoft.com/en-us/sysinternals/downloads/autoruns
I'd also have a look at clock speeds shown in task manager as soon as it opens just to make sure your system is running at correct clock speeds, which during bootup, I'd expect to see 30-40 seconds of clock speeds up to 4.7 GHz while assorted startup tasks are running; being stuck at 800 MHz , on the other hand, could be a symptom of botched chipset drivers, confused BIOS /power saving settings, etc..