I bought the 10Gtek X520-DA1 network cards a few months back because they are cheap 10-gigabit SFP+ cards. Sadly the X520 is quite outdated and driver support on Windows 11 does not come preinstalled (they work perfectly on Linux however). This post likely also applies to the X540, X550, and X710-based cards.
Intel has discontinued these card drivers, removing them from all up-to-date driver packages and the standard Windows driver finder. Batshit insane, but here we are. The only way to get them to work on Windows is to use old Intel NIC drivers.
Here's the download link for the last version that supports the X520. While it lists only Win10 compatibility, the driver works fine for 11, even with HVCI enabled.
In case this link eventually breaks, which it's bound to because Intel does Intel things, here's a direct link to a backed-up copy: https://s3.plasmatrap.com//f3b60a1d-8ab0-419d-a114-850b55c729c5
The .exe is signed by the Intel keys, so you know I didn't mess with it.