It has a dedicated tab just under Unreal Engine in the sidebar. From here, you can access the entire Fab marketplace, browse your library, and make new purchases without leaving the launcher. You can also batch download and export assets in a variety of formats to Unreal, Unity, Blender, 3ds Max, Maya, and Cinema 4D. Houdini and Marmoset Toolbag are not yet supported.

This is apparently the first step toward Fab replacing Quixel Bridge — which will happen eventually — but for now, you can continue using Bridge as you were. Nothing there is changing today. If you're a Bridge user, it's worth reading Quixel's blog post to learn more about the differences between Bridge and Fab, and what their plans are for the eventual transition.

You can also find a list of known issues on the official forum. Look for the Fab in Launcher section under the New and Ongoing Issues heading.

Oh, and in case you were wondering: yes, this means there is another new tab in the launcher that loads another whole separate application with slightly different layout, typography, and UI conventions. C'est la vie.