This has to be just an error the web designer made. Probably copied and pasted old info then added in the new stuff and missed the OS support/
I'm playing Serious Sam 4 right now. It's suppose to be locked to Win 10 but it's running fine on Win 7. I'm using an Nvidia card and Vulcan.
I just checked. There is a Windows 7 driver for the RX 6800XT. I am using the latest Adrenalin 2020 driver on Windows 7 for the RX 5500XT myself right now. But I am using an older Radeon Settings because I think the newer ones stink.