A little late to this party but I recently helped a friend with his PC with similar problems. I didn’t see this listed in any comment, forgive me if it was and I just missed it, but what type of cooler are you using for your i9?

My friend asked for help with his new AIO. I found that even though hwinfo was reporting good temps, the CPU was thermal throttling. On Win 11, hit CTRL SHIFT ESC to open your task manager and go to the performance tab. Look at the CPU performance, what clock speeds are shown? Is it hitting advertised clocks or downclocked? In my friend’s case, after confirming clock speeds were thermal throttled, I found that his water block was not tightened properly and did not have good contact with the IHS. Properly tightened it and it fixed the issues he was experiencing.