I don't know about your board but only the PCIe16_1 and 2 were PCIe 4..
After I set mine up, I decided to try the Z590.. If you have the 3DMark Benchmark, you might want to run the PCIe bandwidth test. I did not do that on mine because I wasn't aware it had that benchmark..
Maximus Z790 Hero,
Intel i9-13900k
Intel BE200