No, you cannot obtain PCIe 4.0 directly from the CPU on X370 boards.
No, you cannot obtain PCIe 4.0 directly from the CPU on X370 boards.
The connection speed would indeed be restricted to 3.0 due to the BIOS settings, not the chipset's capabilities. This applies to lanes from a CPU with 4.0, not the chipset itself.
It would be restricted to PCIe 3.0. Some boards got beta updates that briefly allowed PCIe 4.0, but then AMD stopped supporting it. These devices weren't fully designed for PCIe 4.0 standards, so even if the workaround is possible, performance might not be consistent. They likely avoided handling inconsistent quality and capabilities across boards with the same chipset, plus a push to promote newer hardware.