Doesn’t sound like it. If you put a PCIe 3.0 NVMe in a PCIe 4.0 or 5.0 capable M.2 it continues to run at 3.0.
There’s little real world PCIe scaling data for NVMes and I don’t know of any gaming test that’s stayed consistent across PCIe 3.0, 4.0, 5.0. But what is available mostly indicates for single digit percentage reductions in load time for gen to gen, maybe approaching 20% for 3.0 → 5.0 for some loads in some games.
Possibly. Alder Lake’s been having issues benching full rate 5x4.