Now that have Steam and/or Wine, you now have decent support for running binary only applications. However, there are AppImages and Flatpaks. This book does not and will not go over how to get that support. However, you can figure out how to get that support by looking at another project the GLFS development team works on: SLFS. It has Fuse2 which is required for AppImages. It also has Flatpak itself.
After following the instructions, you should be able to run AppImages and use Flatpak. You can even use Flatpak to install Steam if you wish. That method is not covered in this book.