Do you have an AMD graphics card? And are you on Windows? If so, that's why. Right now, it doesn't work. You can try building a canary build on Linux, where it does work, but the catch right now is that building canary versions on Linux is borked up and thus you can't finish the process (nightly can be built, but the fixes you seek aren't on them).
If you don't have AMD, you'll need to provide people more information than that if you want them to be able to help you, though I believe you'll most certainly get more help over at the
github located here or even at the
discord located here.