hi i have seen in task manger that 1 treath from my CPU is almost not running
14900ks 1 thread won't go 100% in cine bench is my cpu degradated its 0 overclok
Try disabling Windows core isolation memory integrity, Hyper-V and anything else virtualization related.
Someone else recently had the exact same problem you are having. I think his computer magically fixed itself but then later the problem returned. It could be a bug in Windows 11 where tasks are not being properly scheduled on the first thread of the first core. If this was a hardware problem, it would more likely happen randomly on any one of the P cores.