For AMD-based systems, you can plug in a PCIe 4.0 drive and have it run at top speeds on Ryzen 5000/3000 processors. Same goes for AMD's Ryzen Threadripper 3000-series.
For Intel-based systems, PCIe 4.0 support is included on 11th Gen Rocket Lake processors and 12th Gen Alder Lake processors. Just make sure to double check your chip and motherboard online to be sure, as there are always exceptions.