Do B450 Motherboads support PCI-E ?

I believe both slots are generation 3 because chapter 1 of the manual indicates that HP only offered Gen 3 NVMe SSD's in the model series and

2 supports both SATA and PCIe, an module may only be inserted in either one of the two interfaces, so check your motherboard documentation

m2 pcie 40 in 30 slot 2 Is PCIe a bottleneck? Depends on the It'll surely be a bottleneck if you're using a PCIe or card in a PCIe slot

m24 slot Drives typically use x4 PCIe Lanes This can be 4x PCIe Lanes or 4x PCIe Lanes, depending on the Motherboard What