Award-winning Mini-ITX PC case Cooler Master NR200 falls to $51 — its lowest-ever price

Will that PCIe 4.0 X16 riser work in a newer PCIe 5.0 X16 slot and utilize 5.0 speeds?

That case is a nice deal, but if it won't support PCIe 5.0 devices at 5.0 speeds then it's appeal is limited...
 
Will that PCIe 4.0 X16 riser work in a newer PCIe 5.0 X16 slot and utilize 5.0 speeds?

That case is a nice deal, but if it won't support PCIe 5.0 devices at 5.0 speeds then it's appeal is limited...
Nope, it'll run at 4.0 speeds
Not that there are any video cards using PCIe 5.0

The only cards using all 16x lanes of a PCIe 5.0 slot are things like HEDT/server NVMe expansion cards and server grade NICs.