How can I stabilize an HP OMEN 35L if PCIe is running at the wrong generation?

I recently replaced the Ryzen 7 8700F in my HP OMEN 35L with a Ryzen 7 9700X. The system boots and works, but I've experienced stutters, flickering, brief freezes, and occasional hard freezes that remain after reinstalling Windows 11, updating drivers and firmware, and clearing CMOS.

HWiNFO64 and GPU-Z report a PCIe link speed of 32 GT/s, which corresponds to PCIe Gen 5. However, the HP 8CF4 motherboard documentation indicates PCIe 4.0. HWiNFO is also showing very large or continually increasing PCIe error counters, including receiver errors, Bad TLPs, NAKs, and LCRC errors. This makes me suspect that the CPU and GPU are negotiating a PCIe generation the motherboard or signal path cannot reliably handle.

The HP Omen Setup Utility exposes almost no PCIe options beyond Resizable BAR, and I have not found a way to force the link to Gen 4. I also experimented with UniversalAMDFormBrowser, but it did not reveal a usable link-speed setting. Link State Power Management is already disabled.

Before replacing the motherboard or reinstalling the 8700F, I'd like to know what other troubleshooting steps might identify or reduce the instability. I'm also looking for safe ways to force or encourage a lower PCIe link speed without directly modifying the BIOS. Finally, is there any reputable documentation about making small changes to locked-down HP firmware, or would attempting a modified BIOS be too risky even with HP's USB recovery process available? I'm interested in instructions and general guidance, not receiving firmware files or unknown utilities.