Why Am I Getting Low FPS With My High-End Gaming PC?

Hey everyone! I'm facing some frustratingly low FPS in several games, even though my setup is supposed to be pretty high-end. Here's what I'm working with:

- Intel i9-10900K
- NVIDIA RTX 4080
- 64GB DDR4 RAM @ 3887 MHz (had to manually tune it because XMP didn't work; it's rated for 4400 MHz)
- MSI Z590 Gaming Force motherboard (it's used and has some issues, like a couple of non-functional SATA ports)
- 2 NVMe SSDs for Windows and games
- Dual 32" 240Hz monitors (one vertical, which is capped at 60Hz)

Here's how my FPS looks in different games:
- No Man's Sky: about 100 FPS on planets and 150 in space with DLSS enabled.
- Warframe: fluctuates between 100-120 FPS (used to get around 250-300 FPS with my old RTX 2060).
- Minecraft (versions 1.18/1.19): roughly 100-120 FPS on default settings without shaders.
- Only games like Valorant and CS:GO perform at full expected FPS.

Even considering a 10-15% CPU bottleneck, these numbers seem way too low for a 4080. My GPU usage rarely hits 100%, and temperatures are all good.

Here's what I've tried so far:
- Fresh Windows install from a week ago.
- Clean driver installation via NVIDIA.
- Tweaked Windows settings (disabled unnecessary services, enabled game mode, etc.).
- Set power settings to max performance.
- BIOS might need an update, but I haven't flashed it yet because my motherboard is acting a bit sketchy.

Any suggestions on what I might be missing? I can provide logs or benchmarks if needed. It just feels like my GPU isn't being fully utilized!