For a 7900X system with similar cores (non hybrid cores, like in Intel 12th and 13th gen) I would go with Windows 10. Obviously you could "upgrade" later to Windows 11, when there is a reason too, such as you upgraded to a 7950X3D CPU or similar, or Windows 10 is no longer supported.
Also, don't buy Windows from MS. Better to get a good deal on a key site, where you can get them as cheap as $10 sometimes. People tend to be making a big deal out of MS not selling Win 10 keys anymore, but I do believe there are a lot more out there still. And as mentioned, you can often use a Windows 7 key to activate Windows 10 or 11.
Oh, and I will echo that Linux is also an option, if you desire. Certainly has some advantages, but not all software will work on it. Particularly, many games won't, they often prefer Windows.