To really illustrate the difference made by running the RX 6500 XT on a PCIe 3.0 x4 interface, instead of PCIe 4.0 x4, below we can see a chart showing the RX 6500 XT's PCIe 3.0 performance, relative to its PCIe 4.0 performance.
The results are not pleasant viewing. Apart from Hitman 3, where we saw basically no difference between the two PCIe modes, the RX 6500 XT shows clear performance deficits when ran at PCIe 3.0. Forza Horizon 5 is the worst offender, showing a 36% deficit in PCIe 3.0 versus PCIe 4.0, but ten of the twelve games we tested also show double-digit performance losses.