Yeah it's still around, high-contast is an OS-level accessibility setting in Windows.

Here's a Microsoft article about designing for users who have enabled high-contrast mode (technically websites don't need to do anything at all, as the default browser behaviour gives a pretty decent result):

https://blogs.windows.com/msedgedev/2020/09/17/styling-for-w...

Unfortunately, if you want to test high-contrast mode, you'll need a Windows machine (or VM), as Edge doesn't yet have an emulation mode for it (AFAICT), and BrowserStack doesn't let you change OS settings, only browser settings.