Why is my new PC lagging so badly on desktop and in games?

Hey everyone! I'm having some serious issues with my new PC setup, and I'm hoping you can help me out. Here's my build:

- Case: NZXT H6 Flow
- RAM: Kingston FURY Beast 32GB DDR5 6000MHz CL30 Dual Channel Kit
- CPU: AMD Ryzen 7 9700X 3.8GHz
- GPU: Nvidia 3060 ti Gigabyte OC (about two years old)
- Storage: Adata Gammix S70 Blade 2TB NVME (4 months old) and Kingston SATA 3 512GB SSD (around 3 years old)
- Motherboard: ASUS TUF GAMING B850-PLUS WIFI
- Cooler: Deepcool AG620
- PSU: Gigabyte GP-P750GM

Everything is pretty much brand new apart from the GPU and PSU. When first booting it up three weeks ago, everything ran perfectly, but then I started noticing some significant lag both on the desktop and during boot. After some sleuthing, I suspected that the Armory Crate app from ASUS was the culprit. I uninstalled it, and for a short while, things improved. But then, while gaming (like in Helldivers 2 and League of Legends), I experienced dramatic FPS drops and severe lag—everything from the desktop to games felt sluggish.

I attempted a clean reinstall of Windows 11 and redid the driver installs, but the lag returned. No overheating or unusual processes appearing in the Task Manager, and I've also run stress tests showing no problems with the CPU or RAM. Additionally, I plugged in a Type-C wireless adapter into the motherboard's USB-C port, and it made a buzzing noise while affecting my mouse and keyboard. Could that have caused any issues?

I've already tried several fixes, such as resetting the motherboard, updating the BIOS, checking all RAM configurations, ensuring all power supply cables are connected properly, and configuring the BIOS settings. Despite all this, the problem persists. Any insights or suggestions would be greatly appreciated!