Same here. Explorer.exe, i9-9900K, 10%, identical. I took a look at the process via the Process Explorer, and I think the one "iaStorAfsServiceApi.dll!OptaneRegisterListener+0x5a88" and two or three "ntdll.dll!RtlReleaseSRWLockExclusive+0x40" threads are on the top of the CPU usage list and causing the problem.
And while I was writing this comment, I can see chrome.exe is using about 10% of the CPU too. I gave it a check, and bamn, I found the exactly same threads "iaStorAfsServiceApi.dll!OptaneRegisterListener+0x5a88" and "ntdll.dll!RtlReleaseSRWLockExclusive+0x40" on the top of the CPU usage list.
I'm using Optane Memory accelerating my secondary HDD. Restarting this and that didn't help. I tried to suspend these threads and yes, the usage dropped. But the whole taskbar will crash when right-clicked on the icons along with the whole desktop UI. So the threads are critical and I don't think we have a solution here. I hope that we can find the cause and fix it the right way.
Same here too on i7-8700k / Asus Z370-E,
but without any optane disk installed. I only have Samsung 970 NVMe PCIe4x.
I think I've just found a temporary solution. Uninstalling 'Intel Optane Pinning Explorer Extensions' from applications solved these issues.
After uninstalling, my system was idle at 1-2%.